Driving Your Dodge Ram Cummins for Fuel Efficiency!

Moses Ludel · June 23, 2013

In my view, diesel engines and fuel efficiency follow a simple formula: Run the engine as close to its torque peak, and you'll realize the best fuel efficiency.

We have a 2005 Dodge Ram 3500 Cummins 5.9L, stone stock engine, no "chip" or exhaust modifications, the truck is just as it came from the factory (purchased new in fall of 2004). We have a friend with a 2004 model, similar, and we've compared fuel mileage for years now.

I've gotten as much as 25 mpg on an unloaded trip from east of Reno, Nevada to Portland, Oregon. I've pulled a loaded car hauling trailer (Jeep XJ Cherokee on board) to Moab, Utah and managed 17-18 mpg at interstate speeds. Even after "lifting" the truck and adding oversized tires plus enough accessories to push the curb weight above 9000 pounds with fuel on board, I've coaxed 22-24 mpg out of the truck on flat interstate runs.

So, how is this possible? Very simple. I'm an ex-heavy equipment operator and know diesel engines. These engines have a quick torque rise, more so the Cummins among the light truck applications. This means that torque comes on quickly, peaks as horsepower builds, and the overall rpm range of the engine is way less than a gasoline engine.

Note: My lesson for all this was running heavy equipment "in the day", primarily with 1693 Cat engines: At 893 cubic inches, these inline six monsters would reach 1090 lb/ft peak torque by 1000 rpm—that's just off-idle!

Our friend seldom achieves more than 18 mpg from his Dodge Ram 2500. He also has the NV5600 six-speed manual transmission, and I have the "inefficient" 48RE four-speed automatic. What's wrong with this picture? The engine operating rpm and our driving technique differences.

A few years back, I asked my friend what rpm he uses for shift points. His reply was 2500 rpm. The 5.9L Cummins H.O. inline six peaks its torque at 1600 rpm and redlines at 3400 rpm. In my experience, optimal fuel efficiency on the highway with this engine has been in the 1600-1900 rpm range, the best mileage achieved around 1600 rpm when not under load.

Overall, for fuel mileage, the shifts points for this engine should be 1400-1600 when unloaded, 1600 if possible when loaded. There are times, of course, when the 1600-1900 rpm range is necessary to keep a load moving, and even higher rpm may be necessary for acceleration and climbing grades.

When I modified the '05 truck with the lift kit and aftermarket accessories, adding a good deal of weight in the process, the original axle gear (3.73 with OEM tires) was no longer viable. While I believed the "overdriving effect" of oversized tires might benefit mileage, the added load and taller gearing effect actually decreased mileage dramatically—especially trailer pulling.

In selecting axle gear sets to compensate, the new 35" diameter tires required 4.10:1 gears for a direct speedometer correction. I considered the new, unladen weight of the truck and our plans to pull trailers. My choice was to go even lower (numerically higher) on the gearing.

The AAM 11.5" and 9.25" axles do not offer a ratio between 4.10 and 4.56:1, so I went with 4.56:1. This raises the engine rpm at a given speed when compared to the OEM gearing with the original tire diameter. For trailering and the new vehicle weight, I thought the trade-off worthwhile.

Note: Cummins actually recommends 2100-2400 rpm for peak efficiency in commercial use of the ISB diesel engine. They would like to see 2100 rpm at 65 mph and no operating below 1900 rpm under load at highway cruise speeds.

In stock form, 1900 rpm netted approximately 69 mph. Switching to 4.56:1 gearing, 2000 rpm (with overdrive at 0.69:1) nets close to 65 mph. True to my expectations, my peak fuel efficiency is now at 65 mph or lower, a calculated change.

If I hold the truck to 55-65 mph, the unloaded peak mileage is 23-24 mpg. For trailer towing purposes, California caps at 55, Nevada allows for 75 at best, with 65 being plenty of speed for trailer pulling—if you care about mileage...This means watching rpm during upshifts as well.

I'm very pleased with this truck's fuel efficiency. Perhaps a chip could improve this further, although my belief is that driving technique holds far more sway over fuel efficiency than any other factor. If you have a 5.9L Cummins and would like to experience better fuel efficiency, watch your tachometer.

If I creep over 1950 rpm, the price will be a linear increase in fuel consumption. By 2100-2200 rpm, fuel efficiency, reflecting load as well, begins to drop like a rock...

Moses

Megatron · June 28, 2013

This is a topic I need to get in on. I still have stock gearing (3.73 I believe) on my 06 mega cab with 37" tires...Now I get a warm fuzzy when I look at the overhead read out and it says 19, but if you stop, hit the calculator up, and do the math at the pump...well that overhead console is a liar...lol! It's more like 12-15 on a good day.

Now I understand the gearing is a major factor in my situation so I have late summer plans for a set of 4.88's front and rear (thanks to your articles and videos on the AAM 11.5 and 9.25). I have researched a lot, and I believe the 4.88 to be a viable match to the Toyo 37"??

I must admit my build wasn't based on the ultimate mpg, or else I wouldn't be running 37's and a 6" lift, but I don't see why I still can't get the most out of this set up. If there is one thing I have learned about mpg's is speed/rpm. Like you stated above, these things can really make the difference even on a heavy 9000#+ truck.

Moses Ludel · June 29, 2013

Thanks for catching this post...It's among my favorite subjects, as you might have guessed...

Once the axle gearing is correct, the other factors that drop fuel mileage on your '06 Ram 3500 Cummins would be 1) the increased vehicle height (kiss off aerodynamics of any kind!) and 2) the vehicle's weight over stock. I wound up in a similar situation with a 4" lift, 35" tires and a carload of "cool" accessories! Not sure of your accessories, I added approximately 1,350 pounds to my over-the-road, "unloaded" weight...kind of like perpetually pulling a well equipped tent trailer!

Hey, we all like the "look" and utility of a lifted and accessorized Ram 3500 4x4! Here, the truck we purchased new in October 2004 is undergoing a metamorphosis in 2011, getting ready for show time at the BFGoodrich Tires booth, Off-Road Expo at Pomona, CA! Let's see now, the lift, wheels and 35" tires, we'll add a utility fuel tank that takes us to Moab, Utah and back from the Reno, Nevada area...and that M12000 Warn winch will be a dandy when needed! Oops, there went the 25 mpg. Time for a 4.56:1 axle gear change out!

(Can't see the photos? Join our free forums and get the full benefits of membership!)

Most have no idea how quickly the upgrades and accessory weight add up: Try oversized American Eagle wheels and BFG tires for at least 150# over stock including the spare; a Mopar lift kit after swapping out OEM parts for an added 50 pounds; a Warn M12000 winch for 140# (bare winch wound with wire rope); front and rear HD bumpers for an extra 300#; a Transfer Flow cross bed fuel tank with additional fuel on board: 75 gallons @ 7.1 lb/gallon for Low Sulphur diesel = 532.5 pounds when full plus the aluminized steel tank's weight! Oh, and I do like the three Bestop Treksteps for 60 pounds plus.

I'll comment on your gearing projections, just did the math...If your tire's revolutions per mile are around 560 (Toyo rating for several popular 37" diameter tires, confirm your exact revs per mile), then here are your engine speeds at practical road speeds in overdrive (0.69:1):

4.88 gears @ 70 mph = 2200 engine rpm

4.88 gears @ 65 mph = 2043 engine rpm

4.88 gears @ 55 mph = 1728 engine rpm

4.56 gears @ 70 mph = 2056 engine rpm

4.56 gears @ 65 mph = 1909 engine rpm

4.56 gears @ 55 mph = 1615 engine rpm

According to Cummins, you should use the 4.88:1 gears for a truck under 10000# GVWR and intended for 70 mph cruise. In my experience, though, if fuel mileage were your sole aim without carrying cargo or trailer pulling, I would suggest the 4.56 gearing. This would keep you "in the window" for maximum fuel economy. However, even a light travel trailer would immediately tip the scale toward taxing the engine, which could impact both fuel efficiency and engine life—plus overload the transmission (clutch if manual) and driveline.

Actually, with your 37" tires, the 4.56:1 ratio would be much like your 3.73:1 gears with the Ram 3500's stock tire size. (That was also before accessory add-ons and the lift, too!) In overdrive, that off-the-showroom floor truck fell well below Cummins' recommended 2,150 rpm at 65 mph baseline for fuel efficiency and commercial hauling. I'd again emphasize that 23-25 mpg highway was readily achievable with the stock tires, 3.73 gearing and no load at 65-69 mph (approximately 1800-1950 rpm).

If you pull a trailer very seldom and your add-on accessories weight is modest, fuel efficiency would be good between 55 and 70 mph with 4.56:1 gearing and 37" tires. If the add-ons are like mine, however, your truck has a load before you stack on cargo! The 4.56:1 gearing would not be low enough, you'd be better off with the 4.88:1 gears.

Note: This is why I opted for 4.56:1 with the 35" tires, rather than fiddle with 4.10:1, which would have been the direct correction for the bigger tires. We plan to pull a trailer on occasion—without destroying the powertrain. Also, as I've shared, between the lift height and added accessories weight, this is not the stock truck any more.

Your decision comes down to load and intended cruising speed. Considering the height and weight of your Ram 3500 Mega Cab, you'd likely be "happier", performance wise, with 4.88 gears. When you want fuel efficiency, hold the speed to 65 mph. If that's too slow and you want to "cruise" at 70-plus mph yet get the best fuel efficiency for that rate of speed, consider 4.56:1 axle gearing. You can see by the calculations that the engine would be in Cummins' recommended zone of 2100-2400 rpm when cruising at 72 mph (2114 engine rpm) with 4.56:1 gears in overdrive. With 4.88:1 gears at 72 mph in overdrive, the engine would spin 2263 rpm and eat up fuel.

Cruise speeds above 65 mph will eat fuel, regardless...Moving as much mass as our trucks at speeds above 65 mph requires increasingly more fuel. Base your choice on what cruise speed you find acceptable on the highway—the faster you go, the more fuel the engine will use...guaranteed!

The acceleration might be marginally better with 4.88:1 gears. In terms of gear stamina with a given ring gear size (11.5" and 9.25" in our case), the 4.56 gears are actually stronger due to the larger pinion gear head size. (This is slightly offset by the 4.88:1 additional gear reduction, which helps reduce load a bit.) Given our Ram 3500 ring gear sizes, the stamina distinction is not as severe—nothing like sticking 4.88:1 gears in a Dana 35 Jeep rear axle with a 7.625" diameter ring gear!

We can kick this around more, Megatron. Cummins recommends spinning the engine for "efficiency" and, at least commercially, does not want to "lug" the engine below 1900 rpm at highway cruising speeds. Note that a truck under 10000# GVWR with an H.O. 5.9L Cummins ISB engine is less susceptible to lugging than a Cummins ISB engine in a medium-duty truck.

If you're running an aftermarket performance module or "chip", or have done any other tuning or engine modifications, we need to discuss those variables, too...That could change the rpm scale for maximum performance and fuel efficiency, in turn shifting the rpm band for the gearing.

Moses

Megatron · July 16, 2013

Didn't see this reply. Kind of covers my questions on oversized tires lol.

Moses Ludel · July 16, 2013

I must still like writing...Spent time doing a fresh reply at your new questions—guess they're well covered now!

Moses

Megatron · July 17, 2013

I checked my MPH vs. RPM on the way into work today and my truck says @ 65mph I am turning 1750-1800 rpms in overdrive... so ya that's off per the requirements lol. I assume the speedo to be pretty close to correct given a few neighborhood speed trap signs ha-ha. Well I now know I have some work to do in this area.

Ok, I do have a good question. Why does my MPG go up the warmer it gets outside? Does the cold weather rob that much energy from the engine just keeping it warm? Is it possible the winter mix fuels at the pump are less efficient? 5 months ago when it was 20-40 degrees out I was getting 12-13 on the same trip every day. Now that it is 80-90 degrees + out I'm back up to 16-18. I have made no changes to driving style, route or vehicle modifications. Now, I know a little can be lost to letting the truck warm up but even when it was in the 40-50's I wasn't warming up long enough to call it that and I was still getting less mpg. Am I crazy or is there science and math behind it?

I know diesels don't like to warm up a lot in the colder areas and I know the big trucks even run covers on the front of the trucks to slow down air getting into the radiator or engine compartments.

Any input is appreciated. Thanks.

Moses Ludel · July 17, 2013

Thanks for airing these questions, Megatron! Given your truck's weight and lift, as we have discussed, the rpm at 65 mph is too low—but only because of the truck's modified curb weight and wind resistance. I'm not double-speaking, you're at an optimal rpm at 65 mph for extraordinary fuel efficiency with a stone stock '06 Cummins Ram 4x4.

Proof: Before I horsed around with 1200-plus pounds of upgrades and a 4-inch lift, in the summer of 2011 I drove to Portland, Oregon from the Reno, Nevada area for the launch of the Jeep JK Wrangler 2012 model (new Jeep Wrangler 3.6L Pentastar V-6 and other changes—see the magazine's JK Wrangler HD video coverage). I consciously held to 65-69 mph with stock 3.73 gears and tires just under 32" diameter. The truck had its stock curb weight and height (approximately 7,800# unloaded).

Result: I nailed 25 mpg fuel economy from Reno to the mid-Willamette Valley, Oregon! Best mileage on a long trip ever, including climbs over the Siskiyou Passes and the numerous secondary highway grades between Reno and the I-5 access from Highway 89. This was not the "Plains" and surely not one-sided in terms of grades.

That said, if I attempted the 1,600-1,750 rpm under the truck's current curb weight and fully fueled load, worse yet when pulling a trailer, I would expect sluggish performance and mileage. Our Ram 3500 has stone stock tuning to this day, no exhaust upgrades, chips or modifications whatsoever. I drove this rpm range to achieve this exceptional mileage in stone stock form; however, the truck would suffer with that gearing and current 35" tires.

Today, cruising at 1,900-2,000 rpm peak, I can coax 21-23 from the truck with the 9,100-plus pound rolling package, unloaded and fully fueled, driving uniform gradient highways...Managed 23 mpg down the I-5 from Sacramento to the 41 Junction en route to Advance Adapters at Paso Robles in January. Held speed to an agonizing 65 mph to achieve this, got passed like I was standing still by the traffic! Pushed to 68-70 and paid for it immediately: 19-20 mpg with 35" tires, 0.69 overdrive and the 4.56:1 gears.

Last year's trip across northern Nevada's I-80, through Elko to Salt Lake City and on to Moab, I did manage 22-23 mpg at 65 mph on I-80. Frankly, the Bonneville Salt Flat and Great Salt Lake Basin is tortuous at this speed, although I did have plenty of big truck company in the slow lane. This is the price for maximum fuel efficiency. Diesel engines are rpm and load sensitive! For that matter, gasoline engines fare as bad or worse under load.

We really enjoy the truck and its "look". (Objectively, folks at trade shows and the Moab Jeep Safari rubberneck to see this Ram 3500 Quad Cab, as I'm sure they do your Mega Cab!) To a degree, I'm willing to "pay the price". However, my days of 70-75 mph trailer-toting with the XJ Cherokee on board en route to Moab, expecting 17-18 mpg, are over. I'll still expect 15-16 mpg with a trailer in tow, fully loaded, but only after my change to 4.56:1 gears and "governing" speed to a maximum 65 mph when towing. Wind is a much larger factor with the 4" lift and 35" tires, an obvious fuel mileage variable...

As a footnote to the trailer toting mileage, I lugged a toy hauler to Johnson Valley for the 2012 King of the Hammers race week coverage. I still had the OEM 3.73 gearing (like you do) and did respect California's strictly enforced 55 mph speed limit for trucks and trailers, holding speed to a limp along 58-59 mph peak. I thought the mileage would be great. Wrong—mileage fell to 12-13 mpg, the worst ever for this truck's trailer pulling and a 7,500# (loaded) trailer. It's all about the right gearing and keeping that diesel happy under load!

This raises a point we haven't touched yet. You're weighing the 4.56 versus 4.88 gearing choice for your 37" tires. How about this idea: Install a Gear Vendors overdrive behind the transfer case! The auxiliary overdrive only works in 2WD High range, but you could run 4.88s or, better yet, 5.13 replacement gears in the AAM 11.5 and 9.25 inch axles with the use of the Gear Vendors overdrive when practical—including split shifting on grades with a trailer load. See the interesting torque gains described at the Gear Vendor's website. I've linked directly to the Dodge Ram section.

Gear Vendors is a 0.78 ratio or 22% overdrive, which could only be used minimally in tandem with your 0.69 overdrive gear. Final drive equivalent in overdrive/overdrive would be 5.13 x .69 x .78 = 2.76:1. This compares to 4.88 x .69 = 3.36:1 [48RE overdrive without Gear Vendors OD]; or 5.13 x .69 [48RE overdrive without Gear Vendors OD] = 3.54. Your OEM gearing factors currently as: 3.73 x .69 = 2.57. Of course, we haven't targeted engine rpm and your tire diameter yet...We can play with the gearing equation and see if this makes sense.

Cost aside, the Gear Vendors overdrive is a consideration if you're on the fence here. ..I've got a one-piece driveline at 140.5" wheelbase, you're longer based with a two-piece driveline. Plenty of room for a Gear Vendors unit in either case. For my truck with its current 4.56:1 gearing and 35" tires, I'd have gains like 1) the double overdrives when running empty at cruise or 2) when pulling a hefty load, I could use the Gear Vendors overdrive with the 48RE in 3rd gear (22% versus 31% overdrive, a 9% reduction advantage). You haven't changed gears yet, so there are more options to consider.

I like your seasonal fuel efficiency question! Like the intercooler, winter cold air creates denser oxygen content, which increases power. If your climate is humid in the summer, you may get an additional intake air cooling effect and, therefore, denser oxygen content in the intake stream. A denser charge means improved combustion and, at least theoretically, better fuel efficiency if you can keep your foot out of the more responsive throttle!

Another factor to weigh is the OEM or aftermarket computer "chip" tuning that takes advantage of a denser IAT reading by changing injector pulse width. This could also work another way: When winter intake air is cold and dense, the injectors flow more fuel to create the right air/fuel ratio. The result is more fuel consumption and peak throttle response.

I believe the winter fuel efficiency loss is also due to lubricant viscosity and cold pour, especially in the axles. (Transfer case lube and ATF are now largely synthetic and wider-range viscosity, typically with a lower weight ceiling.) It's no small fact that OEMs now use lighter, multi-viscosity lubricants for CAFE ratings. The AAM axles call for 75W-90 weight lube. My choice of running 75W-140 Mopar gear lube for severe duty use may, in fact, create a loss in fuel efficiency—especially in the winter.

Don't get carried away with this factor, though, unless we're including engine oil viscosity. See this technical paper for interesting details on fuel efficiency as it relates to motor oil viscosity: http://www.instituteofmaterials.com/paper/FEIPaper.PDF. I'm running Mopar 15W-40 year round with use of a winter block heater to avoid startup damage. Frankly, this could be a source of higher fuel use in winter. The 5.9L Cummins engine can drop from 195-degrees F to the bottom of the temp gauge during a 30-minute groceries stop!

Another factor, perhaps significant in our case with oversized tires, is rolling resistance. In winter, the advertised or usual static cold tire pressures can create drag. On frigid highways in chilling air, the tires do not reach the predicted temperatures for pressure calculations. In the summer, there is less rolling resistance as inflation pressures rise due to ambient and road surface temperature increases. Sadly, tire pressure is fixed (unless you have a Humvee and can air and deflate on the fly!). You cannot inflate tires to the summer over-the-road pressures for winter use—the tires would be deformed and wear quickly on their tread centers from "over-inflation". They would also be a terrible hazard with minimal road surface contact!

As for engine operating temperatures, and this is a factor, it does take "forever" for the Cummins engine to warm when ambient temp is sub-zero to 40-degrees F. This is not a coolant thermostat issue, although 18-wheeler shutter-stats like you hint would be helpful. The Cummins ISB engine has a huge cooling capacity! Forget letting the engine idle to warm up, it will take forever to reach operating temperature.

On that note, I'll emphasis that I do use a block heater all winter. The truck is not a daily driver, but on any day with a planned run, I plug in the block heater the night before. Under a carport with a Battery Tender hooked up whenever the truck parks, let's say it is a 10-degree F morning: The engine coolant's startup temperature will be around 120-130 degrees F with the block heater.

Warmer weather (a whopping 35-degree F, let's say), start-up temperature will be around 140-degrees F. That noted, I start the engine and always wait for the oil to circulate sufficiently before rolling. It will sometimes take from Fernley (home base) to four miles West on I-80 before the engine reaches thermostat temperature. During this entire time, I hold engine speed to no more than 1,500 rpm under light throttle load. I expect this diesel engine to last for 500,000 miles, enough to bury the initial cost difference over a gasoline engine—and also to save a small fortune through fuel mileage gains over that number of miles.

So, summer does bring better fuel efficiency. In my case, I've also switched to GDiesel, a natural gas altered fuel. (See my coverage of GDiesel in an article and HD video interview at the magazine.) By breaking down long chain molecules to more combustible form, this fuel does deliver mileage gains. Even better, I do not engulf other motorists in soot when I launch into the throttle during passing.

Yes, my truck's exhaust, even without the later catalytic converter and exhaust stream additives, is clean, without visible smoke—black or white. While some clean-up can be produced through ECM programming, that's only to a degree. I use GDiesel and avoid mixing it with conventional low-sulfur fuel. (GDiesel is actually the very same low-sulfur base fuel, reprocessed with a patented method. You can mix the two in a pinch.) Fortunately, I can make it to Moab from Fernley and back home on one fill of the main tank plus the 75 gallon auxiliary Transfer Flow tank in the bed.

Thanks for the questions, Megatron...Others are welcome to jump into the discussion and share their experiences!

Moses

Megatron · July 18, 2013

Okay, I am onboard with the Gear Venders overdrive setup. While it has an initial cost, it is one that can truly be paid back during its service if better fuel mileage is achieved. I have an Atlas 4SP transfer case with a similar unit on the input side for reduction. I am aware of how they work and mine works fine (on my rock-crawler not my daily driver, although I thought about putting it in my truck. You have given plenty for me to research, and research I shall do!

Your points about winter fuel mileage make sense. While I had hoped I could point my finger at one thing and fix that, you have shown it is a multiple of things adding up. I do switch to different oils for winter time, but I was under the impression it was spec'd from the factory this way?

Your GDiesel is something I have never heard of. I am only a year into the diesel world so I still have much to learn. I plan to check this out as well. I am a fan of science and am amazed how it can effect my wallet on daily driving.

This may be a dumb question but I thought I would ask, hope it makes sense. At what speed do you think "lack of" aerodynamic efficiency rules out any attempt to be fuel efficient? Now this is not something I can test given my local speed limits, but with my current truck gearing I should be running in the 80mph range (-/+) to be at the desired RPM for engine efficiency. Do you think that I would see a fuel mpg increase at those speeds, hypothetically? At least if I get a speeding ticket I could say I was trying to save some money lol.

My next real question, that I hope you may have experience with, is water/methanol injection for MPG gains. Have you gone this route yet or maybe anybody that is reading this? The science seems to be there and the posted research seems to back the claims, but I have reservations about the on going cost to replenish the supply vs. the gains. At some point you have to say your still spending money on the 2-3 mpg you saved but is it still cheaper than the price of fuel?? Are there other gains besides a rusty intake plenum that you can take into consideration?

As always, thanks for your knowledge and insight on all topics. You are definitely filling my brain with knowledge that is useful and I plan on putting as much of it to use as possible.

Moses Ludel · July 19, 2013

Well, you're certainly opening my eyes to the value of humor in these posts! Keep it up, Megatron...

The Gear Vendors is definitely an option to consider before you change axle gears. Here's some quick math on the Gear Vendors 0.78 ratio overdrive with your 48RE automatic transmission and a change to 5.13:1 axle gearing: At your favorite highway cruise speed of 75 mph, if you use the Gear Vendors overdrive plus your 48RE's overdrive, with 37" tires (560 revs per mile) and 5.13 axle gearing, your engine speed would be 1932 rpm.

From my experience with our 3500, this could be close to the optimal cruise rpm for maximum fuel efficiency at this weight, height and speed. If you needed passing or pulling power, without the need to floor your 48RE for a forced downshift to third gear, you'd simply kick out the Gear Vendors overdrive and be at 2478 rpm.

This is the best of both worlds and does target your 75 mph cruise speed. If you slow down to even 70 mph, you'd be at 2313 rpm with the 48RE's overdrive and direct gear on the Gear Vendors. Apply the 0.78 Gear Vendors overdrive, and engine rpm would drop to 1803 rpm. You get the picture, this looks like some targeted rpm options for optimal fuel efficiency and still above the torque peak rpm in all cases.

By the way, it's very nice of me to help spend your income on items like a Gear Vendors overdrive! Kidding aside, this could pay big in fuel savings and also offer some incredible torque and pulling options as a split-shifter. Neither you nor I currently have the advantage of the latest 8-speed automatics—unless you toss the Gear Vendors overdrive into the equation! This is the wave.

Again, here is a copy of the Gear Vendors link I provided in my last missive: Gear Vendors overdrive when practical. Gear Vendors is in the gear business, and they build an impressive case for torque gains through nothing more than gear ratio changes and split shifting. The OEMs have obviously gotten the message with the new wave of 6- to 8-speed automatic transmissions—which will make manual transmissions in light- and medium-duty trucks a thing of the past. Before taking the plunge, consider your GVCW (gross vehicle combination weight) with the trailer in tow and the stamina you can expect from a Gear Vendors overdrive.

As for winter oil changing and specs, consider the wide range of climates and engine operating temperatures that OEMs address. Oil recommendations must be generalized and take into account the temperature range from startup to warmed operating temperature under load. Dicey choices! 0- or 5-wt. motor oil is great for cold pour in Alaska—but not for the very same engine running at 195-degrees F thermostat temperature once it warms up. Minus 50 F to 195 F is a wide temperature range—from cold start to fully warmed up—a typical Fairbanks, Alaska day in the dead of winter!

Regarding the 80 mph method of getting the engine to rpm, save the speeding ticket. (Try running to 80 mph on some secluded road and let me know whether the engine likes it...Watch your rear view mirrors for flashing red and blue lights.) Note that when you increase load like with a trailer in tow, you may need horsepower in addition to torque. The Cummins 5.9L ISB engine is under no stress at stock 7,800 pound curb weight and OEM height; loping along at 1,600-1,900 rpm seemed just fine under that scenario, with road speed peaking around 69 mph.

To push our "billboards" down the road at 80 mph creates high rolling and wind resistance. You did the math perfectly for your 37" tires, 3.73 stock gears and 80 mph in 0.69 overdrive: 1,922 rpm. The question is whether the engine would be happy at that rpm under heavier loads.

I used to periodically run our truck to 100 mph in a sprint up a particularly secluded highway in the desert. The grade was over 6%, and I would start at the bottom around 65 mph and accelerate to 100 before the crest of the relatively short grade. With the truck's current weight, the lift, tire drag and even the right axle gearing, the engine would perform this feat under load now—even with nothing in the bed but the auxiliary fuel tank. Times change—we still like the look and utility, though, right?

Now we're talking about the constraints that drive Cummins to declare that our engines should never run below 1,900 rpm under load, and they want to see us running 2,100-2,400 rpm with "commercial" loads. Driving your lifted truck 80 mph is a pretty good load, perhaps comparable to "commercial use" standards.

Here's engine performance data on the Cummins ISB 24-valve 5.9L inline six: http://www.cumminsdieselspecs.com/24v.html. Our engines peak their horsepower around 2,900 rpm. Most ISB commercial applications have 3,200 rpm governors. Chrysler and Cummins added a couple hundred rpm for those Ram owners who think they're driving a gasoline powered vehicle, even though the engine's power has fallen off considerably and shifting to the "next gear up" would be a better idea.

The horsepower rpm is worth considering. While peak fuel efficiency at a light load is 1,600 rpm, without getting into physics, we can assume that if we continue adding a load to the engine, we will need more horsepower. An H.O. engine peaks at 325 horsepower, quite impressive and requiring 17.2:1 compression. So, you're right in suspecting that as the load rises, fuel efficiency suffers.

Of course it takes more power to move over four and a half tons of mass at 80 mph. Then there is the aerodynamic (lack of?) drag coefficient we know is lurking. In terms of drag coefficient, all I could drum up on line was for a stone stock model year 2000 Ram 3500 4WD Quad Cab: 0.48 rating. If you'd like to see how this stacks up against other vehicles, ranging from sleek race car models to popular econo-boxes designed for peak fuel efficiency, or even some SUVS (much like our trucks), check out this well-done Wiki entry: http://en.wikipedia.org/wiki/Automobile_drag_coefficient.

The cool thing about the diesel engines in our Ram trucks is that the torque stays well up there from 1,600 rpm to at least 2,700 rpm! This means that unlike a gasoline engine, the torque and horsepower don't go separate ways with advancing engine speed. Diesel technology does require a re-think on the part of gasoline "performance" enthusiasts who see horsepower figures as an end all: Unlike diesel torque rise, high horsepower figures are only attainable at higher rpm.

This even applies to the popular Jeep 4.2L/4.0L hybrid "stroker motor". Begin with a reliable inline six. Build a "hot" stroker for 300-plus horsepower, and discover that to achieve this kind of power, you'll be pushing the torque and horsepower peak rpm way up the scale. Here are figures for an exotic Jeep 5.0L stroker gasoline engine built from a 4.0L inline six block with a custom stroker crankshaft and 11.5:1 compression: 344 horsepower @ 5300 rpm and 384 lb/ft torque @ 4000 rpm. Great performer for sand drags—lousy power curve for the Rubicon Trail!

The analogy for a Cummins diesel is that maximum high performance/horsepower builds (those short lifespan engines that Gale Banks talks about) mean spinning the engine to oblivion to achieve peak power. Gone is the famous torque rise that distinguishes a long stroke commercial diesel engine—or a stock 4.2L Jeep inline six for that matter—from the typical gasoline engine...

Regarding the principles of water/methanol injection and its history, here's a nice ditty: http://en.wikipedia.org/wiki/Water_injection_(engines ). A water/methanol injection kit like the one offered by AEM reminds me of one of my earliest freelance magazine pieces. We had a '73 Chevy K10 4x4 SWB pickup with a 350 V-8. I installed a "solution" injection kit that was popular in the '70s. That somewhat sophisticated system came with a thick carburetor base gasket that had small orifice tubes running into the throttle bores.

A needle bleed valve at the glass solution jar metered the water/alcohol mix. A slight bubbling indicated proper adjustment and flow. Pretty slick, actually, the device did what water and alcohol/methanol injection will: On a gasoline engine, it cooled and condensed the incoming fuel/air charge, reduced ping or detonation, allowed for more spark advance and better power, and permitted use of higher compression ratios. Such a device allows fuel timing and compression changes on a diesel as well.

Not often mentioned, during the combustion process, the water/alcohol or methanol solution will remove carbon from the combustion chambers, valves and piston crowns. Upon the 350 V-8 teardown, the cylinder heads and upper engine looked virtually "new". In this modern era of electronic fuel and spark management, carbon buildup is a virtual non-issue. In the era of the Quadrajet carburetor, however, fuel enrichment and "venturi effect" made carbon deposits at the upper cylinder and combustion chamber areas a chronic engine problem.

Fuel efficiency improved dramatically, the 350 V-8, gasoline powered truck delivered as much as 18 mpg with 3.08 gears, a 1:1 fourth gear ratio in the SM465 four-speed and 33" diameter tires. Performance improved noticeably from added spark advance—without signs of ping/detonation.

For your diesel, this injection would act like an additional intercooler, keeping exhaust gas temps lower for less stress when trailering or hauling a load. The upper engine would be cleaner, possibly extending engine life. As with GDiesel fuel, crankcase contamination from incomplete combustion would be decreased. Combustion would be more thorough.

Is this enough to outweigh the cost of methanol/water injection? Can't say for sure, but this is why I buy GDiesel locally for 10-12 cents a gallon more than other low-sulfur diesel pump fuels. I'm "banking" on the engine yielding a cleaner tailpipe, cleaner crankcase (lab tested the oil at Pape Cat, it's holding up much longer and shows fewer contaminants at change intervals) plus extending engine life. If water/methanol were used for this purpose, I might buy it...

Moses

demerchant · March 25, 2014

Moses, Megatron,

First off well done. I have to say after hunting for quite some time that this thread holds some of the most pertinent and well put information that I have been able to find. I have an '02 3500 ram dually that I tow with delivering travel trailers and 5th wheels across the country. I put a lot of miles on and half of that time under load of generally 8 to 15,000 pounds of tow weight. I have the automatic transmission and 4.10 rear end. I am no mechanic and a lot of what I read is greek to me so I'm hoping to get some advice from those that I believe are in the know.

I drive dead heading with my RPM set at 2000 splitting the line which my gps reads out at 65, and towing as well with my O/D on unless i'm pulling mountains and then I turn it off only when the hill starts and I know its enough to drop my gear and turn it back on when I crest. I'm making 19-20 miles per gallon (on my overhead display) dead heading and 10 (average) when hauling despite the weight. This is with the truck fully stock (25 gal, reserve tank in the bed, no tailgate). This weekend I went out and upgraded the exhaust to 4" from the turbo back with an aero muffler and picked up a K&N filter (despite some folks dislike of them, only ever had good luck myself). I am hoping to see some better fuel efficiency from the move but both were out of necessity (exhaust rusted out and I got tired of paying for a paper filter every-time).

I am only looking for efficiency as it affects my bottom line. I have no interest in increased power or noise, in fact I almost went stock with the exhaust system again for that very reason, I have to be able to live with the truck spending 11 hours in the seat a day and sleeping in it more than occasionally. This seems long winded, so I'll get to it, I'm looking for advice on fuel efficiency, i.e. -maintenance practices, upgrades, and most importantly driving techniques, I have no idea what my optimal peak RPM is? and with that being said, longevity of my truck is foremost. I would like to see her join the million mile club someday. Let me know what ya think...

Moses Ludel · March 25, 2014

Welcome to the forums, Demerchant! I'm pleased to see your Ram delivering such good service and mileage. The weight involved is phenomenal, a real testimonial and chapter for the "Cummins story".

As for maximum fuel efficiency and longevity of the engine, you're on the right track. Your K&N choice did come with the general concerns about gauze filters and adequate filtration. You drive highway, however, so dirt is not as much of an issue. The exhaust upgrade should be a plus, certainly no down side. If you continue to drive for economy and not to "see what the new exhaust and K&N air filter can do for performance" (well, maybe a little bit, but at the sacrifice of mileage when you do!), then these add-ons will be help with engine breathing and exhaust flow.

Your 19-20 at 65 mph dead heading in overdrive sounds reasonable. The dually weighs a bit more than our '05 Ram 3500 SWR, and at 65 mph with 3.73 gearing, no load (also before the auxiliary fuel tank, massive winch/bumper, etc.) and stock tires, I could squeeze 23-plus mpg highway most of the time. I did accomplish a one-time high of 25 mpg on the highway, achieved by keeping the engine between 1600-1900 rpm faithfully over a 480 mile trip.

Again, as Megatron and I have discussed, engine rpm is the key to fuel efficiency with any engine, and in particular the Cummins diesel. Our '05 HO reached peak torque (stone stock) at 1600 rpm, and driving between 1600-1900 was the sweet spot. If I pushed beyond the 1900 mark, fuel efficiency dropped considerably.

When I added 1200 pounds of accessories and auxiliary fuel, the new dynamic, plus oversized diameter tires, required 4.56 gears. I'm now in the same league as your 4.10 gearing with your stock tire diameter. 69 mph is now 2100 rpm. 65 mph is a hair below 2000 rpm (1980-1993 rpm depending upon accuracy of the current tire diameter). 65 mph will return a consistent 21 mpg on highway cruise without a trailer, even at full fuel load (110 gallons) and the truck's weight hovering around 9,000 pounds. 69 mph means 20 mpg, often dipping to 19.8 mph with hilly or mountainous highway terrain.

You're already driving for economy at 65 mph peak. If your tires are stock at around 31.9" diameter, with 4.10 gearing and 65 mph, I have the calculation at 1937 rpm in overdrive. (Does that sound right?) This is near the magic zone of 1600-1900 rpm for the later 2005 HO 5.9L ISB Cummins.

As a comparison, the 2002 Cummins HO and standard engines reach stock peak torque by 1400 rpm. (Please confirm whether you have the 250 hp "standard" output engine. As I understand, the 2002 HO 305 hp engine was available only with a manual transmission, not your 47RE automatic.) Chrysler kept the lid on peak torque output with the 47RE transmission then turned the torque wick up on the 48RE with advertised horsepower at 325 and 610 lb-ft torque. (This is wonderful as long as the transmission can stand it! If we had not purchased our truck for multiple drivers, I would have opted for the 6-speed manual transmission.) Your 2002 Ram 3500's peak torque should be 460 lb-ft. (The HO with manual transmission rated 555 lb-ft in 2002.) Torque peak for both the 2002 standard and HO engines was at 1400 rpm. Our 2005 peaked its torque at 1600 rpm in stock tuning.

An interesting footnote is how flexible the power can be on these Cummins diesel ISB engines. The 2002 HO's 555 lb-ft torque was quite a boost over the standard engine. Most of this difference is tuning or tune programming for these common rail, electronically fuel injected engines. When I decided to reprogram the '05 engine with a Hypertech Max Energy tune, the torque peak went up, achieved at 2100 rpm instead of 1600. This was a boon, as the engine now reaches peak torque at 68-69 mph and can deliver 20-plus mph on the highway even at that rpm and road speed.

Torque peak is the key to fuel efficiency on these engines. Theoretically at least, your engine and fuel economy should be best between 1400-1800 rpm. A test for improved fuel efficiency might be to drop your cruise down to 1800 rpm (59 mph or so) and check the mileage. It should go up. Even slower, like 55 mph (1700 rpm), should deliver better mileage yet.

This raises a practical consideration, though. Try confirming my suggestions for improving mileage on a flat stretch of road when you have the time and patience! Since there is also the sensible need to drive your truck at a reasonable pace, you may find that saving fuel is less important than getting to your destination in a reasonable timeframe.

Note: According to Cummins' commercial site, the ISB commercial version of this engine should be run between 2100-2400 rpm for maximum efficiency (presumably including mileage). That's with commercial engine tuning/programming and intended loads to 50,000 GVCW. In my experience, that rpm would drop the mileage to the 17-18 mph range unloaded. With commercial tuning, however, it might help the heavy hauling tow mileage.

There are few design differences between our engines. Hypertech taught me that tuning is everything: power, fuel efficiency, rpm for peak torque and peak horsepower. (Click here to see my full explanation of the re-programming approach.) A Max Energy program for your engine could make a difference in two ways: 1) an overall increase in performance and 2) bumping the peak torque rpm up, which would make your 2000 rpm cruise speed more viable for fuel efficiency. Understand that with any diesel engine, shoving more fuel and air into the engine increases power and often efficiency. I'm not clear about the number of miles or wear on your engine, and if you consider a re-program, do not alter your driving habits. Keep a lid on the engine exhaust temperature (EGT) under load!

This last point is crucial. Hypertech assured me that its programming is "tow friendly". Your scenario would be the ultimate test, considering the loads you pull! I would not do a program change without installing an EGT meter. This should read exhaust temperature at the pre-turbo point if possible to assure an accurate read of actual exhaust temperatures. The turbo can cool exhaust readings considerably, so "post-turbo" probe installations can often be inaccurate.

Warning: Use extreme care with drilling into the manifold pre-turbo: Metal filings and residue can destroy the turbo! Some use grease on the drill bits and tap. (Some argue this is not a good idea.) There are other techniques we can discuss if you install an EGT kit yourself.

This sums up as two options for better fuel efficiency: 1) slow down the engine speed (either lower the vehicle's road speed or install a Gear Vendors overdrive for dead heading) and/or 2) do a tuning program change like the Hypertech with the proviso that you monitor your EGT as a safeguard. We're all on board with making the "million mile club" with these trucks...If you need an incentive, just price a new Ram/Cummins 3500 dually!

As an anecdote from third parties, I was parked at a local fueling station alongside two Dodge Cummins trucks (an '04 and '05). The owners, a father and son, commented that our 5.9L models get much better fuel efficiency than the later 6.7L models. Better yet, and consistent with your plans, they had an '02 that ran to 600K miles before selling it, and the father insisted that the truck is still out there doing fine. It had a "chip", the type and brand not discussed, and according to these fellows, the mileage and performance were impressive. All three of their trucks were automatic transmission models, there was no discussion about transmission rebuilding.

Let's keep this discussion going, Demerchant. The cost of fuel won't be going down any time soon!

Moses

raccoonjoe · April 4, 2014

Moses:

I'm a camper jockey the same as Demerchant, and I could use some help.

Truck specs are as follows: 02 Dodge 2500, 8' box, quad cab, 4wd, 3.54 gears, 250k miles. Completely stock, with the addition of a low fuel pressure light, a ScanGauge II, and a Smarty S03 programmer set to level 3 (towing). I also have a FASS DDRP lift pump, and a bed mounted 50 gal. fuel tank. Empty weight (without the bed tank), loaded with my gear, was about 6600 #.

The best fuel loaded economy I've managed was 14.3, running from IN to NC with a strong tail wind. Empty? Maybe 22 mpg. Averages are usually more like 10.5 loaded and 18-20 empty. Round trip mileage usually comes out to 14.

Loaded speeds are kept to 60-62 usually, downshifting to 3rd when climbing hills. I set the cruise at 62 when I'm running home empty. This keeps my rpm around 1600 in 4th. I lower speed in 3rd, according to the mountain I'm trying to climb, usually 50-55

I'm struggling to get good mileage out of this rig. I started in this business running a worn-out Chevy 2500 2wd, with a 6.5TD. I bought this Dodge a few months ago, hoping for more mileage and easier towing. The Chevy would deliver 22-24 empty and 11.2 loaded, consistently, driven the exact same way. I dropped a pretty penny on this truck, because it had a reasonably straight body, new factory transmission (with single disc billet TC), and a completely rebuilt fuel system (new stock injectors, VP44, and DDRP lift pump about 2 years ago.) I'm planning on adding a FASS Titanium 150 LP when I get my taxes back for longevity and reliability.

Really hoping to have a million mile motor on my hands, but I've got to do something about fuel economy. Fuel prices are bad enough here in IN, but I spend most of my time in The Great White North, where fuel prices *start* at $5.25/gal. I had this crazy idea about lowering the truck, but can't figure out how to get around the issue of oil pan-front axle clearance.

Thanks in advance

Paul

Moses Ludel · April 4, 2014

Hi, Paul, welcome to the forum posts! To begin, the weight of your truck as equipped may be higher than 6600# when "empty". Is this over-the-scale weight or speculative? Our '05 Ram 3500 4WD Quad Cab SRW with short box was somewhere around 7,800# advertised curb weight. I've searched around the internet, and owners and information sites are throwing out figures of 7,100 to 8,100 pounds for stone stock vehicles, not being clear about completely empty or with passengers, fuel and so forth. I think we need to weigh our trucks, calculations for my truck are not actual scale weight.

So, it would be wise to start with an accurate weight figure, and if you get one, please share. (We'll start using actual weights rather than advertised or speculative weights.) Also, I'd like to know the loaded truck weight whether it's in-bed campers or travel trailers in tow.

I understand your frustration and am looking at your gearing. 3.54 is tall. Our truck had 3.73 gears when new, and without all of the add-on weight of accessories (lift kit, tires/wheels, Warn massive bumper and winch, Transfer Flow fuel tank for 75 gallons more fuel and so forth), we consistently got 22-24 mpg at 65-69 mph. At the conservative speeds you describe, running empty, I would achieve 24 mpg or a bare minimum of 23 mpg.

If your tire size is the same as our '05 was stock, you should get better mileage than you're finding. Before commenting further about your tall gearing, I would like to know the tire diameter/size. 3.73 gearing seemed the magic number for our stock '05 tires at 65 mph, I caught an all-time best of 25 mpg with this arrangement on an empty run from the Reno Area to Portland, Oregon, holding speed to the 65 mph range. This was one time.

Gearing is crucial. With the added equipment, weight and oversized tires, which essentially gave me gearing more like yours would be with stock tires, the fuel efficiency actually fell off. I thought optimistically that the overdriving effect of the 34.6" (advertised 35") tires would possibly improve mileage, and it didn't. Fuel mileage dropped dramatically, especially when trailer pulling.

So this tells us something about the sensitivity of gearing. For the oversized tires, 4.10:1 gears would have restored the rpm and load to stock, but I wanted more pulling ability for the added weight and anticipated trailer pulling. There were no AAM gear sets available at the time between 4.10 and 4.56:1, and after pondering quite a bit, I opted for 4.56 gears. (You can see my install article and video at the magazine site, use the term 'AAM' in the Search Box.)

I knew it would be necessary to hold speed to 65 mph for fuel efficiency, 69 is tops now, and my mileage varies accordingly: On flat ground, 65 mph is good for a consistent 21 mpg average with full tanks of fuel, passengers (2), luggage, empty bed and no trailer in tow. I've "squeezed" 23 mpg on flat I-80 runs with a tailwind at 65 mph. Step up to 69 and pay the price: Mileage is more like 20 mpg and drops to 19 in hilly country. Emphasis is that the truck could weigh over 9000 pounds going down the road "empty" as described. (Again, I need to get valid scale weight here!)

3.54 gearing is quite tall, however, your engine has a different torque peak speed (lower) than our '05 HO. Not sure what the dyne figures show for the "Smarty" reprogramming, if you have peak torque ratings from their testing, we can take that into account.

I'm not comfortable spending others' money and time on gear changes unless there would be obvious gains. Please clarify your loaded weight (estimate at least), whether you are hauling in-bed campers or travel trailers, the tire size and the torque rating with the Smarty programming. Also, does the 'ScanGauge II' include a pyrometer? We'll discuss this further...

Moses

raccoonjoe · April 4, 2014

I'll do my best here.

The ScanGauge provides readouts from the truck's OBDII system. (https://www.scangauge.com/products/scangaugeii/ for reference). I use it to keep tabs on IAT and coolant temps, as well as a "guessimate" of mpg. (All of my mileage figures are hand calculated, from the same station, same pump, unloaded every time. I fill up at the beginning of every trip, and log fuel purchases and mileage until the next time I can fill up at my favorite station.)

The 6600# weight was from the scale at my local gravel pit. ~30 gals of fuel, driver + passenger, my toolbox/chains/straps/etc onboard, but not my 50 gal aux tank. My scale ticket from Alberta on 4/1/14 says 1960 k (4321#) front axle, and 1350 k (2976#) rear axle. Truck, with me, my gear, and about 50 gal. of fuel onboard, no trailer. That is a certified Canadian scale, so it's probably the most accurate. Total weight of 7297 pounds.

Tires are Firestone TransForce A/T, 265/75R16, on stock steel rims. About 50% tread, run at 65 PSI.

I run bumper pull travel trailers or horse trailers. Usually no 5th wheels right now, no in-bed campers at all. Curb weight and sizes will vary, from 2000# up to 10,000#, 20' to 37'

I just bought this truck a couple months ago, haven't had time to get it completely outfitted yet. I've got a set of gauges, boost/pyro/temp. The only one installed right now is a trans temp gauge, mounted in the pan. The others should be going in this week, as I've got some time off. I will also pull a diff cover (probably the front) to verify the gear ratio of 3.54.

I'm also going to try and make a couple of pulls on the dyno at a local automotive college. I want to make a pull with stock ECM programming, as well as a couple with the Smarty on different settings.

I don't have much experience with these trucks, having mainly run bigger, IH and Cat motors in my past, where fuel efficiency wasn't nearly as much of a concern. I know there are aerodynamics issues with this big of a truck, things that I will be addressing. My only other comparison is word of mouth from other drivers. Just met another yesterday, with an identical rig, except 2wd. He claimed to get 14 loaded, 25 empty, but didn't have any numbers to back it up. YMMV, as they say

Moses Ludel · April 5, 2014

Paul...I'd cleave toward the Canadian readout of 7,297 pounds, still less than I expected. The tires are stock size and like my '05 before the change. You're running a lot of pressure when empty, so they have more than enough air. (Are you okay with running this kind of pressure empty, or do you drop down to door sticker settings?) Sounds like you're pulling good size trailers but not pushing "billboards" down the road as far as wind resistance goes; the tall 5th wheels are the billboards.

Would like to hear if the gear ratios on the axles are other than 3.54:1. Glad you're into the pyrometer. When running aftermarket programming and these kinds of loads, you do need the EGT monitoring to keep a lid on the engine stresses. EGT is the best means for monitoring the load on a diesel. I need to get a pyrometer for the '05.

Really would like the dyne results from the community college testing, how fortunate that you can use this dynamometer. Stock would make sense as a baseline. This is exciting, Paul!

The 25 mpg is not out of reason for a 2WD empty with the correct gearing. If he drives like we do, for mileage, 25 is conceivable. I place great stock in the right gearing, the Cummins ISB engines are hypersensitive to rpm when it comes to fuel efficiency. Under commercial loads (to 50K GVCW, apparently a medium duty truck application, not my one-ton with a 48RE transmission, for sure!), Cummins would like to see the ISB engine running in the 2100-2400 rpm range. I wouldn't expect more than 17-18 mpg unloaded and 14 mpg pulling a 7,500# trailer at that rpm. When I push to 2100 rpm empty, which is actually my presumed torque peak with the Hypertech Max Energy programming, I can expect 19-20 mpg, depending upon terrain and wind.

This last factor, wind, cannot be underestimated. I raised the truck 4" with a chassis lift and added oversized tires, which is clearly a red flag for fuel efficiency. These trucks are hardly aerodynamic to begin, and I asked for it with this move. Since all modifications to my truck were made simultaneously, there is no way to separate the impact of the lift and broader frontal area, i.e. increased wind resistance, from the rest of the changes.

For that reason, I work with the known factors: 1) driving for efficiency is something I can control, 2) gearing is intended for a top speed of 69-70 mph if fuel efficiency is primary, 3) gearing (4.56:1 with 34.6"/35" tires) was picked to maintain the lifespan of the engine first, as a fuel mileage consideration second, and 4) I take full responsibility for the impact of the lift, tires, gearing and all the accessories added to the truck! This last point is an important qualifier. I can't complain about fuel mileage after doing all of these modifications intentionally. I'm in damage control mode at this point.

Let's keep working on your mileage. I appreciate your approach and the information gathering that you're willing to do. We can work with these facts and find a sensible strategy.

Thanks!

Moses

raccoonjoe · April 27, 2014

OK, after a bit, I'm back.

I took my truck to the local dyno, and got some mixed results. I was having troubles with the transmission wanting to shift, and it was giving me some mixed readings on torque and horsepower numbers. Basically, every time the transmission would shift, it would peak the torque curve. This seemed to happen about 2200 rpm or higher, under WOT.

The closest thing I can guess, I did have a few runs that showed a peak torque between 1800 and 2000 RPM. I'm working on a few other sources of info, to see if I can get any more accurate information. May also be able to make another dyno run in a few weeks.

I had a issue with fuel pressure up in North Dakota last week, ended up installing a FASS 150 Titanium lift pump. Truck is running great now, but for some reason my fuel gauge doesn't work now. It seems sometimes that if it's not one problem, it's another, right?

On my last run back from Colorado, I seemed to get the same ~20 mpg whether running at 70 mph (1900 rpm), or running 65 (~1750 rpm). I know that going from fillup to fillup across states isn't the most accurate method of measuring, but it's what I have to work with.

While regearing axles isn't really in the cards financially, I will be needing to replace my tires in the next few months. This should allow me to go smaller to adjust for the gear difference, if necessary.

Moses Ludel · April 27, 2014

Umm...For the stock ECM, the 1800-2000 rpm torque peak is higher than expected. This would be closer to an aftermarket tune or programming. Dyne tests by Hypertech on the program now in the '05 Dodge Ram 3500 show peak torque at 2,100 rpm; Chrysler factory programming was rated for peak torque at 1,600 rpm. My fuel efficiency sweet spot, again, is 1980-2000 rpm maximum, which would have the torque at or near peak. This is a reasonable road speed of 65 mph.

It is not surprising that you would get 20 mpg at both 70 and 65. The rpm range may reflect peak torque versus lower engine speed. Typically, mileage does improve with less speed, but if torque falls off too much that is not necessary the case.

In considering your quest for maximum fuel efficiency, aside from correct gearing and tire diameter, another aid is a conversion from unit hubs and the front axle constantly spinning to freewheeling hubs. A full-floating hub conversion (resembling the "real" 4x4s of a bygone era) allows use of freewheeling hubs to disconnect the drag of the inner axle shafts, differential gears and front driveline when in 2WD mode at the transfer case. Manual freewheeling hubs make this a true disconnect, and the full-floating spindles, wheel hubs and inner/outer wheel bearings offer superior load carrying capacity and lifespan. This setup also allows for periodic wheel bearing service/lubrication like traditional 4x4 axles.

The frictional loss with our trucks' current unit hub bearing and axle shaft arrangement is "parasitic" drag. To what degree full-floating wheel hubs and freewheeling hubs would improve mileage is uncertain, though. The cost of the conversion is substantial and needs to be weighed. Amortizing the cost in fuel savings might take a long time.

Dynatrac makes a quality conversion kit for our Dodge Ram trucks. See the link below for details:

http://www.dynatrac.com/products/freespin-dodge/freespin-dodge.html

Mose

raccoonjoe · April 29, 2014

Real quick, before I end up forgetting. I spent a long time talking to Cummins, he told me that in stock form my truck makes 440 torque @ 1600-2100, and 235 hp @ 2300-2700 rpm. Im still waiting to hear back from Smarty to figure out what their programmers will do.

Moses Ludel · May 7, 2014

Interesting...Factory Chrysler "tuning" drops the torque peak rpm down to the lower end of that spectrum...Usually, de-tuning of an engine takes powertrain stamina into account. The automatic transmission versions of these Ram truck diesels tend to get the lower performance ratings during these model years. The 46RE, 47RE and 48RE transmissions are clearly not candidates for competition "puller" torque, and that's likely the reason for the de-tuning.

What's interesting is the potential horsepower and torque latent in these Cummins engines. The basic paradigm with a turbocharged diesel is that the more fuel flowing into the engine, the more horsepower and torque. Exhaust temp goes up commensurate to the amount of fuel getting shoved into the engine, so there's a limit to the power boost that the engine will tolerate. For a Cummins ISB, this is all adjusted by the tune: boost, injection timing and fuel flow.

Trade-offs are that de-tuned means less power but also less EGT. Most likely in the case of light-duty trucks with diesel engines, the torque peak is also regulated to keep transmissions, drivelines and axles alive...

Moses

hertfordnc · June 8, 2014

Hi, I found this thread in a google search on Cummins MPG and joined this forum specifically to get in on this discussion. I think I read everything above a couple times. The idea of running at peak torque makes so much sense I can't believe I have never seen it anywhere before.

I just bought a 2003 Dodge 3500 with NV5600. The goal is to make it an efficient daily driver and trailer puller. We have a 7000 lb vintage camper so it's no problem for the truck.

I am most interested in fuel efficiency when running empty. My daily commute is 26 miles with just a few stops and turns on 55 MPH back roads.

I put on a set of used matching tires sized to the door sticker (235/80/17)

The MPG you describe above, is that calculated at fill up or based on the computer? So many people on these forums talk about mileage without making that clear.

Do you think switching to single wheels would help? There is a lot of un-informed debate about that.

What about modifying the fan? Again, in my reading I find a lot of misguided uninformed debate. I know electric fans are theoretically more efficient, but the debate over making it work on a fully laden Dodge 3500 on a 7% grade is too much for guys on a forum to unpack in a linear way so it's hard to get clarity. In my case, I have no plan to get anywhere near this trucks max capability so I can afford some degradation of performance in change for efficiency.
If not an electric fan, are there thermostatically controlled clutch fans that perform better than OEM?

Hope to hear from you.

Thanks

Dave

Moses Ludel · June 9, 2014

First of all, thanks much for joining our discussion. The more folks who share their real world experiences, the better. All of us will gain in the long run.

To begin, I've learned that the only valid mileage check is actual gallons used versus the miles traveled. The odometer must be accurate, and that should be checked separately from the speedometer. I emphasize this because we're all inclined to think that an accurate speedometer calibration automatically means an accurate odometer reading. It doesn't always work that way.

The easiest and least expensive odometer check is the official five-mile test on an interstate or highway that has accurate markers in place. If you can hold the throttle (cruise control helps) steady at 60 mph, this can also be a quick speedometer check: At 60 mph, each mile should be exactly one minute on your watch's second hand.

Once you have the odometer's accuracy confirmed, you can check fuel mileage by accurate fuel fill-ups. The factory digital mileage meter can then be compared to real world gallons burned over X-number of miles.

As for single drive versus dually, any mileage difference should reflect vehicle weight savings, and little more. If there is a frictional loss issue with dual tires per side, I have not heard of significant gains with a single drive rear wheel setup. In talking with many Dodge Ram 2500 and 3500 owners, both SRW and DRW (3500) trucks, fuel mileage does not seem to follow rear wheel layout with any consistency. This would suggest that axle gearing and tire diameter, vehicle height and mass, accessories added, driving style and other factors hold more sway. The reason for dual rear wheels is safety if you plan to load the bed heavily or pull a hefty conventional trailer or especially a larger fifth-wheel trailer.

Electric cooling fans are not a free ride, as they draw amperage from the electrical system and alternator. Although the amp draw is not severe, as would be the case with an onboard frequency welder or other high-amperage draws, it is measurable with regard to engine load. Before arguing that an electric fan eliminates the "parasitic power drain" of the factory mechanically driven fan, turn your attention to the CFM flow of each and the amperage load.

Note: The engine driven fan can pull a huge amount of air through the radiator when the fan clutch couples. It is only in recent years that the very best electric fans and shroud systems have approached this CFM flow.

Personally, I prefer an engine-driven mechanical fan with a clutch unit. As you hint, a thermostatic fan clutch can be improved upon, and I have used high performance aftermarket fan clutches to great advantage. If you take this approach, be prepared to live with the sound of the fan coupling up at unanticipated times. Most truck fan clutch thermostats or viscous fan couplers respond to hot air coming through the radiator core—rather than a specific engine coolant temperature.

The reassuring part of this process is to watch the coolant temperature drop immediately when the fan noise occurs. For this to happen, the radiator and water pump must have sufficient flow rate in GPM/GPH, and the radiator must have enough tube and fin surface area to dissipate the maximum BTUs produced by the engine under full load.

A great advantage of a fan clutch is its overrunning, freewheeling or uncoupling ability at higher rpm. Without uncoupling, a fast spinning fan and a vehicle at increased road speed would be at odds with each other. Ambient air rushing through the radiator core could get blocked by the high speed fan, and this obstacle to air flow would decrease cooling ability.

An aftermarket electric fan is often either on or off, regardless of road speed or the volume or velocity of ambient air flow through the radiator. The signal for an aftermarket electric fan is either coolant temp or radiator surface temp. Once on, the fan spins at a fixed speed regardless of road speed.

My approach for maximum cooling has most often been an engine driven fan and a substantial shroud. I've built oversized shrouds to capture the radiator's entire surface area heat, capturing and directing hot air toward the fan. This eliminates hot air stalling and radiator hot spots.

Next, the heavy-duty fan clutch must be thermostatically controlled to come on at a temperature that will keep the lid on the engine's upsurge of heat under load. This is even more critical with a turbo-diesel's boost and instant increases in exhaust temperatures. I am comfortable with any power loss caused by a mechanically driven fan. If I can keep the engine temperature under control, the gains far outweigh the fan drag!

Here is just one example of a thermal type heavy-duty fan clutch: http://www.summitracing.com/search/product-line/derale-performance-fan-clutches/make/dodge/engine-size/5-9l-359/engine-family/cummins-diesel/clutch-style/heavy-duty-thermal.

Regarding quick heat surges, the factory's omission of a pyrometer on our Ram trucks is an area of concern. I do intend to install a pyrometer (properly, and we can discuss the correct approach). I plan to use the pyrometer to achieve maximum performance without shortening the engine's life. While the tachometer keeps us in touch with the torque peak, a pyrometer lets us know when to back out of the throttle and stop stuffing fuel into the engine under boost.

From what you describe, and assuming you have 3.73 or 4.10 axle gears with the stock diameter tires, you should readily get 22 mpg at 55 mph. Running empty when our Ram 3500 was strictly stock, I did even better than that (23-25 mpg) when I carefully followed the tachometer during upshifting and through each of the gears.

The easiest place to gain mileage is through driving technique. Find your engine's "sweet spot" for fuel efficiency. I'd suspect it's around 1600-1800 rpm on an '03 5.9L, that's at least a place to start. Once you achieve your best mileage run and benchmark, stay within that rpm range whenever practical. Straying from the sweet spot will cause an immediate drop in fuel mileage.

Lastly, there are the aftermarket improvements that can keep the engine alive and still boost performance and fuel efficiency. In hindsight, I would say that the most significant impediment to my truck's fuel efficiency was not the added weight of accessories (though that's surely a factor) as much as the chassis/tire lift and the large winch bumper, which amplified the truck's exposed frontal area.

The overall effect was an increase in drag coefficient. I've actually gotten 25/26 mpg with this truck in its current profile (running empty) by simply catching enough tailwind to offset the frontal drag. I did drive within the engine's sweet spot to achieve this fuel efficiency.

We can and will discuss this further. There are always "trade-offs". A lift kit and oversized tires can be much like a cabover camper or travel trailer: Any of these factors create drag that often mimics a billboard getting pushed down the road!

Moses

hertfordnc · June 9, 2014

I think part of the advantage some people get from electric fans is simply settling for less cooling. For vehicles that are not run at the limits of their capability eliminating the parisitc drag and replacing the cooling with a less capable fan will result in some gians, right?

What about dropping the final drive to 3.42? I know, crazy, but follow my particular logic;

I know i have 3.73 gears now. Where I live and where i would do my daily driving is pretty flat. The NV5600 give me lots of choices to match RPM as needed, I could start using 1st and 2nd more.

This is more truck than i need. It happend to be a very good deal, it's cosmetially bad and mechanically good (far as I can tell) But it's a lot of truck. I would have chosen a 2500 or Ford F250 or perhaps a Diesel suburban. But I wound up with this truck for just over $4K so if it works out I will modifiy to suit my needs and I don't care if i degrade it's overall capability.

My camper weighs 7200 lb. With 3.73 gears this truck is rated at 13,800 lb.

With stock tires I beleive 3.42 gears would turn 1900 RPMs at 72 MPH.

I see people discussing the idea but I have not seen anyone post results.

Your thoughts?

Thanks

Moses Ludel · June 10, 2014

Hertfordnc...I followed a similar logic when 35" tires and a lift kit gave my wonderfully fuel thrifty '05 3500 an "overdriving" effect. I harbored the illusion that the 3.73 gears with these new tires (similar to your current tires and 3.42 gearing) would possibly improve the mileage!

My first real experiment was pulling a toy hauler to the King of the Hammers Race at Johnson Valley, CA in 2012. To that point, I had speedometer error and other challenges that kept me from seeing the light. The trailer was the capper, though. I had formerly pulled our XJ Cherokee on the car hauling trailer (open deck) to Moab and saw the mileage with the stock truck and 3.73 gears go from consistent 22-plus mpg running empty down to 17 mpg at interstate speeds (to 70 mph) and 6% grades while pulling the trailer. I thought this was enough mileage drop until I tried the 35" tires with the 3.73s!

Towing the trailer loaded (8,500 pounds approximately) at mostly 55-60 mph, the mileage dropped to 10-12 mpg. This did include the grades along U.S. 395 and on I-15, so we're certainly not talking about "flatland" towing. Nonetheless, this was the worst mileage I have ever experienced with our Dodge Ram 3500.

I switched my thinking to trailer towing needs and our anticipated use of a travel trailer. The gearing choices at the time were 4.10 or 4.56, nothing in between, with 4.10 being somewhat close to OE with the stock tires and 3.73 gears. A true "correction" gearing would have been more like 4.30:1, which AAM axles did not offer at that time. (They do now.) So, I opted for 4.56 gears with the pledge that I would gear for 65-69 mph or approximately 2000-2100 rpm. This rpm was slightly high for stock but consistent with the Hypertech Max Energy program I installed at the same time.

1980 rpm is the sweet spot now for keeping up with traffic and still getting reasonable fuel efficiency. I pulled a 9,000 pound trailer over the I-8 grade from La Mesa, CA to the Anza-Borrego Desert this winter and managed 14-15 mpg, very respectable considering the load and a series of mountain passes.

So, my guess is that 3.42 gears won't cut it, and you will be using all five gears on a regular basis! Mileage will likely drop off. In perspective, a friend just bought a new manual transmission 2014 Ram 2500 4x4, and it came with 3.42 gears and a six-speed. He's thrilled so far, and we'll keep tabs on his success with this tall gearing. Oversized tires would naturally be out of the question, even with the 6.7L engine. The 6.7L engine has a catalytic converter and urea downstream system. Arguably, the 6.7L will not "outperform" our 5.9L engines, which came stock with no cat or urea system. My '05 HO rated 325 (some say 305) horsepower and 610 lb-ft torque in stock form.

I have considered a Gear Vendors overdrive behind the transfer case. I have a 140.5" wheelbase and single piece rear driveshaft that could be readily shortened to accommodate the overdrive. Here is a listing for our trucks: https://www.gearvendors.com/ag4x4.html. Though pricey, the overdrive/underdrive would be like going to taller gearing while retaining the current axle ratios as well. Another distinct advantage is gear or torque splitting with this overdrive...Here is more Gear Vendors info for the Dodge Ram trucks: https://www.gearvendors.com/d2wd4s.html.

Photo Courtesy of Gear Vendors

Some things to ponder, Hertfordnc!

Moses

Moses Ludel · June 10, 2014

As a footnote, you benchmarked 1900 rpm at 72 mph as a possible target goal for fuel efficiency, Hertfordnc. We're all familiar with "lugging" an engine, and under load and weight, that 1900 rpm could demand considerable turbo-boost to achieve 72 mph. We also need to look at boost curves, since loading the engine triggers turbo boost and injector flow, which directly bears on fuel efficiency...A boost gauge would clarify the function of turbocharger boost under load.

Keep in mind that our engines are not just diesels, they are turbo-diesels that derive considerable power under boost. This requires more fuel, though, as there's no such thing as a free ride. The assumption is that a properly gated and meted boost will help performance and fuel efficiency if not abused. To maintain proper air/fuel ratios under boost, however, does require more fuel to match the additional, compressed air.

Moses

hertfordnc · June 10, 2014

But aren't we talking about the same thing? It was the use of the 3.42 gears on the newer trucks that got me thinking about this. I'm not as co ncerned with towing mileage as I won't be towing that often.

The other five gears would still give me plenty of choices.

What am I missing?

Moses Ludel · June 11, 2014

In my two replies, my concern is that taller gearing, in this case 3.42:1, might actually cause a drop in fuel efficiency due to more turbo boost and fuel flow needed to power the load, whether the truck is towing or empty.

In my first reply, I indicated the mileage drop that resulted from 3.73 gears and 35" tires, something like a change to 3.42 gears with stock diameter tires. Mileage was lower for both trailer pulling and when running empty. Mileage was off because the engine worked harder and used more boost/fuel despite the lower crankshaft speed.

I added the information on Gear Vendors overdrive to show how you can keep your existing 3.73:1 axle gearing yet have an additional overdrive. The Gear Vendors is a 22% overdrive, which would be the same as dropping 2000 rpm down to 1560 rpm. You would still have the 3.73:1 gears when needed and could use all of your current transmission gears plus split-shifting between these gears. The links to the Gear Vendors information includes an explanation of the torque gains when split shifting.

As for the late trucks with 3.42:1 axle ratios, these models also have a six-speed manual transmission. The transmission gear ratios differ from your NV5600 transmission. 2003 NV5600 Dodge Ram transmission ratios:

1ST 5.63

2ND 3.38
3RD 2.04
4TH 1.39
5TH 1.00
6TH 0.73
REVERSE 5.63

2014 Ram Truck 6.7L Cummins with G56 Six-Speed Transmission Ratios:

1st 5.94

2nd 3.28

3rd 1.98

4th 1.31

5th 1.0

6th 0.74

Reverse 5.42

Axle ratios 3.42, 3.73

On the 2014 Ram with 3.73 or 3.42 axle gearing, the first gear ratio is slightly lower than your '03 NV5600, frankly not enough to impose an excess load if you do change to 3.42 axle gearing. If tire diameters are the same, you might "get by" with the 3.42 gears, although your engine torque is not as high as either my '05 HO engine or the 6.7L late model engine. (Your engine's torque peak is 555 lb-ft if an HO engine; SO engines were only 460 lb-ft. Confirm which engine you have here, Hertfordnc.) The 6.7L and my '05 5.9L HO each produce 610 lb-ft torque maximum.

If you do have less engine torque, the 3.42 axle gearing could be too tall. The engine would labor, boost would go up, and you could lose mileage rather than gain it. 3.73 is fairly tall gearing for a 1-ton truck; 3.42 is even taller and requires more torque.

Assuming that you don't tow much and can use the gears properly, the truck might tolerate 3.42 axle gearing. You would be working the transmission's lower gears more and downshifting more frequently. Even running empty, my gut choice would be 3.73 axle gearing for a truck of this weight and stock tire diameter.

The tallest factory geared, manual transmission truck I owned was a '73 GM K10 4x4 SWB pickup with 3.08s and a 350 gasoline V-8. It did not have an overdrive, and the SM465 transmission's 1st gear ratio was 6.55:1 with a 1:1 fourth gear. The truck did deliver decent fuel efficiency and even tolerated 33" diameter tires. Starts in second gear (3.58:1) were possible when running empty or a lighter load. When empty, that truck was at least 1500 pounds lighter than your Ram 3500 dually 4x4.

There's also another way to simulate taller gearing, and this might be a consideration: Change to a larger diameter tire. Without lifting the truck as I did to install 34.6" diameter tires, you could step up with a tire that will fit the stock rims and still clear the fender wells without the need for a chassis lift. Pick the right tire, and this could be a subtle change that would drop engine rpm some. Tire clearance with the body and frame would set the limit on tire size.

You would need to recalibrate the speedometer to compensate, and this is a function in the PCM under ABS module. If you're curious about Ram truck speedometer calibration, see my video coverage at the magazine: http://www.4wdmechanix.com/How-to-Dodge-Ram-Speedometer-Calibration.html. I also talk about how to determine speedometer error in another video. While a dealership can calibrate the speedometer with a DRB-III scan tool, many aftermarket engine management programmer kits have a speedometer calibration function as well. I can calibrate for tire diameter with the Hypertech Max Energy programmer (see details at the magazine).

Moses

hertfordnc · June 16, 2014

Moses,

THanks so much for your advice. I've been working hard at shifting in your suggested RPM range and getting pretty good results. Topped off the tank, drove 100 miles or so, computer said 21.7 actual was 19.9; topped it off again and now the computer is holding around 24.0 . My other car is a hybrid so I'm pretty familiar with the issues of driving technique but the explanation of torque range really brings it all together.

WHat about performace upgrades that do not dump more fuel in the can?

Bigger exhaust, cold air intake, etc. People usually do those thing to shred tires and scare small animals and then they lie about the the MPG. But do you think those upgrades would actually help if I did not want to shred tires?

thanks

Moses Ludel · June 17, 2014

You're welcome, hertfordnc! Once you start driving this way, it becomes habit. "In the day", I tested a lot of trucks for magazines and newspapers, we were always about performance, mileage came under discussion in passing. Today, mileage is a topic of interest for all but a few!

Bigger exhaust and cold intake do offer gains, although fuel mileage improvements might be incremental when considering the way we're both driving these trucks. There's a caveat here: Why would a vehicle manufacturer, bent on meeting CAFE standards for fleet and seeking fuel efficiency bragging rights, consciously avoid mileage gain strategies? Packaging a vehicle does face constraints and tradeoffs, and maybe bigger or space consuming improvements like you mention simply will not fit, or they create assembly challenges.

Exhaust being "bigger", unless scavenging gains are clear, has little impact beyond irritating your neighbors when you come home late at night. Loud exhaust tones have you idling out of the neighborhood when your trip begins before dawn.

As proof in my case, I got the best mileage to date with a stone stock truck. The Hypertech Energy Max programmer was to offset the downside of a chassis lift (the increased frontal drag) and nearly 1200 pounds of really neat accessories and auxiliary fuel now on board that is equivalent to pulling a tent trailer all the time.

The truck runs fantastically, but the power is now further up the rpm scale with peak torque around 2100 rpm. Just the increase from a stock 1600-1900 rpm sweet spot to accomplishing the same road speed at a higher rpm (thank 4.56 gears for this) is enough to burn extra fuel. In fairness, this was not anywhere near an apples for apples test, the truck has too many changes to draw comparisons from stock.

So, when it comes to fuel efficiency versus "performance", Chrysler and Cummins did a good job on these trucks. Driven like a "truck" and not a county fair puller, you can get good mileage. I had the 3.73 gears with the stock tires and did very well for overall fuel efficiency, hauling ability and performance.

Keep driving on your best behavior and see what this package can do for fuel mileage. You may be at peak or near peak right now...At least you'll have a true benchmark with this consistent driving style. If you can get 22-23 mpg at reasonable road speeds, that's about it, frankly.

My best of 25 mpg was at 55-65 mph, empty, stock curb weigh, no lift kit or auxiliary fuel tank, and holding engine speed precisely between 1600-1900 rpm. Interestingly, that trip included mountain passes, so the mileage was apparently influenced more by engine rpm than load.

Moses

hertfordnc · June 17, 2014

About that ideal range of 1600-1900 RPMs, which side do I err on?

I spend a lot of time on 50-55 mph two-lane country roads. so I'm at 1970 RPMS in 5th at 50, 2170 RPMs at 55. But I'm at 1500 RPMs in 6th.

I'm leaning toward staying in 5th longer. What do you think?

thanks

Dave

Moses Ludel · June 18, 2014

Hertfordnc...Stay in 5th longer, there's no gain to "lugging" the engine...When you can stay above 1600 rpm in 6th, use it...

Moses

hertfordnc · July 10, 2014

Just back form a 1500 mile trip in the 6000 lb family car (2003 dually 4 door) and I have an obeservation about the clutch fan:

The truck temp hovers at 200 degrees and the clutch fan sometimes kicks in when I'm cruising at 60+ it goes off after a few minutes. Assuming this is normal that means that 60 mph does not deliver enough air to keep the engine cool (outside temp around 100 F)

Every square foot of open grille equals 5000 CFM at 60 MPH so an electric fan would have to move north of 10,000-15,000 CFM to equal that, right?

Oh yeah, i got 19.9 miles on the best 350 leg of the trip (not hurried, rested, no traffic) I got 18-19 on the rest of hte trip.

Moses Ludel · July 29, 2014

The mileage and fuel use is well within norms, at interstate speeds, 19.9 works for me these days!...The cooling is interesting. Good that the fan wants to cycle before engine temp gets excessive. Fans operate from either a coolant sensor at the radiator or block, or they are self-contained with their own thermal sensor for coupling.

I like fan clutches that have thermal couplers. Like the Hayden high performance type and similar designs. They can be quite noisy but at least move air and clear the hot engine bay. We had a Suburban 4WD 2500 series with a small-block 350 V-8 gas engine, a heroic pushrod motor that delivered extraordinary service for its displacement and gasoline design. When the OE fan clutch wore out, I replaced it with a Hayden that made a lot of noise when it came into play but also cooled that engine dramatically and in a hurry!

What I don't like is a total dependency on electric fans, although the Spal fans in the XJ Cherokee work flawlessly. You cannot pull the CFM with electric fans that you can with an engine driven truck fan. The game is all about CFM flow, radiator flow and dissipating BTUs as quickly as possible.

I doubt there is an electric fan that could match the ambient air flow rate you describe. If there is, the amperage draw would require a huge alternator and energy drain on the engine! Years ago, I had a Toyota Land Cruiser project for a magazine and installed an electric fan system (no engine-driven fan) from a popular manufacturer. I discovered that at 30 mph, it made no difference whether the fan was on or not, the engine cooled the same. This was the radiator quality and size, plus good ambient air flow.

Moses

belizeancowboy · October 22, 2014

Hi. I find it very interesting to read about fuel efficiency. My truck is a 03 2500 dodge 4x4 quad cab cummins with 35" tires 3" lift with some aftermarket upgrades like afe cold air intake, 4" exhaust aeroturbine banks tecnicooler air ram, BD super turbo single, BD exhaust manifold, snow performance water injection kit, 50 hp injectors, smarty programmer running it 90hp up, 4.56 axles, Garmon 48re trans triple disc converter.

I have a hard time to get more than 15 MPG that's running empty between 65 to 70 with lots of slowing down and speeding up on a 250 mi. trip with a little heavy right foot. So I'm thinking all my upgrades don't help me much for fuel efficiency other that it is a fun truck to drive with all the power it has. All those after market parts sure don't help as much for fuel efficiency as advertised to my opinion.

Moses Ludel · October 22, 2014

Fully understand your point, belizeancowboy! Horsepower and torque equal fuel consumption on a diesel. The more fuel you cram into the engine at a given compression ratio and injector timing, the more horsepower. You're making fantastic horsepower, I'm sure! The price tag is fuel consumption with this tune.

Do you have a pyrometer on the exhaust system? What kind of temperatures are you seeing at various throttle positions and loads?

Sounds like a fun and fantastic Ram 2500. Please share photos and upgrade/modifications at the "Garage"! We'd all enjoy seeing your truck...

Moses

TaylynQuay · October 22, 2014

I drive a 2008 Dodge Ram 3500 Cummins. It has a 4-inch lift, Mud Grippers that are 35's, stock exhaust, no chip or delete. What would be better to do for better fuel mileage, should I just put a chip in it or put in cold air intake, straight pipe it, take the catalytic converter off? Or if you have any better ideas, please help.

Moses Ludel · October 22, 2014

TaylynQuay...Welcome to the forums, we're very pleased to have you join the Dodge Ram/Cummins discussion. There is a lengthy topic aimed right at your fuel mileage questions. Please read through the popular (over 22,000 visits as of today!) exchange at our Dodge Ram Cummins forum: http://forums.4wdmechanix.com/topic/89-driving-your-dodge-ram-cummins-for-fuel-efficiency/.

If you have any questions or comments after reading through the posts and replies, just ask or post! Looking forward to your participation.

Moses

TaylynQuay · October 23, 2014

Thank you! That helped me out a lot! Appreciate the information

Moses Ludel · October 23, 2014

You're welcome, TaylynQuay! Looking forward to your solution to the mileage issue. My comments about axle gearing should resonate...At 35" tires, I'd probably opt for 4.30:1, a ratio not available when I took the 4.56:1 route. 4.10 would be a direct tire correction if you have 3.73 gears now and not too many aftermarket add-ons beyond the stock curb weight...

I may fiddle with 36" or 37" diameter tires if the fitment is right with my 4" lift. (That's likely pushing it!) This would shift "gearing" toward the 4.30:1 realm.

Moses

connercop · November 4, 2014

Moses,

I have been reading your thread for a while now. I have a 2006 5.9 Cummins with a 6 speed. I had to do the tachometer repair because it is (was) one of the 2006 models with the tachometer issue. Now that I have repaired the tachometer, I noted that 65 MPH for me is between 2000 and 2100 RPM. I ran the truck empty for 400 miles on one tank at 65 and was able to achieve 21 MPG. It is a short bed, 2WD 4 door. It would appear I have .411 gears? Is there a simple way to check using the VIN or similar? The tires are 26570R17. The door label says the tires should be 26570R17 and an "E" added at the end. I pull an 11000 LB trailer most of the time when I drive the truck and am wondering if a taller tire would help (or hurt) the mileage. Your thoughts?

EDIT: I found a PDF here

http://www.dodge.com/bodybuilder/2006/docs/intro/vin.pdf

that tells you about the VIN. Apparently the VIN does not change when the rear ratio changes. In fact, I could not see where the transmission type was included in the VIN either.

Moses Ludel · November 7, 2014

Hi, connercop, pleased to see your participation at this topic! First off, glad you had the tach corrected, as these engines and fuel efficiency are very closely related to engine rpm, load and road speed. You should have a tag on the rear axle indicating the ratio, and if not, at least a code tag. Please share that information and indicate whether you have a manual or automatic transmission. If an automatic, it will be the 48RE that we have in our '05 Ram 3500 4x4. The manual is likely an NV5600 six-speed...Please clarify. If you are running 2000 to 2100 rpm at 65 with stock tires in overdrive, I am reasonably certain that you do have 4.10 gears and not 3.73.

Regardless of transmission type, a taller tire might help if you do have the 4.10 gears in the AAM 11.5" axle. If you have 3.73 gears, common with the automatic and your tire size (which was my OEM, too), a taller tire could actually hurt mileage, as I've clarified in posts above. Especially with the 11,000 pound trailer, taller tires that effectively act like a taller axle ratio, would place a greater load on the engine and geartrain. We do far less towing with our '05 3500 4x4 and have only pulled a load like yours a few times. Most of our trailering has been within the 5,500-8,000 pound trailer weight range.

The 21 MPG empty at 65 is less than the peak I achieved when our '05 was totally stock and had 3.73 gears with the 48RE automatic transmission. if your road was essentially flat, with no headwinds or other load variables, I would expect 23-24 MPG running empty at that road speed. That stated, with an 11,000 pound trailer in tow, 3.73 gears would likely deliver much poorer towing mileage than the 4.10 gears. In a nutshell, heavy loads and taller gearing (numerically lower) are not practical. Increasing tire diameter then towing your 11,000 pound trailer loads would likely result in poorer towing fuel mileage as well. Add to this the extra load on the powertrain.

The stock peak torque point with your truck's 5.9L is fairly low at 1600 rpm. I would assert that taller gearing or larger tires would be tolerable and actually increase fuel efficiency when running empty. (Stone stock truck with 3.73 gears, I always achieved the best mileage between 1,600-1,900 rpm, the closer to 1,600 the better.) Pulling a trailer with taller gearing (axle ratio change or larger diameter tires) would tax the powertrain, though, and likely produce poorer fuel efficiency when towing. Especially with the 48RE, I would not do the larger diameter tires or a gear change to 3.73 ratio if pulling an 11,000 pound trailer regularly.

All of this considered, you might benefit from the Hypertech 'Max Energy' reprogramming as I did. (Click here for the HD video and article I did at the magazine on the Hypertech Max Energy programs for the Ram/Cummins and Jeep 4.0L. The Ram coverage applies to your engine and powertrain.) This torque and horsepower boost also pushes up the peak torque rpm to 2,100 rpm. This is where you currently drive and perhaps want to tow with your truck. The program boasts being "tow friendly", though I cannot substantiate this from personal testing, we don't tow an 11,000 pound trailer with the '05 and the Max Energy programming. If I were to use the Max Energy full-performance mode (which I currently do on my Ram 3500) and planned to tow beyond our current 8,000 pound trailer weight limit, I would install an engine pyrometer on the exhaust manifold (pre-turbo side at the manifold's higher heat point). I'd want to monitor the exhaust temperature and use that as a "barometer" for when to back my foot out of the throttle and protect the engine.

Here are the official specifications for your 2006 Ram truck, scroll down for Cummins 2500/3500 details: http://www.media.chrysler.com/dcxms/assets/specs/2006DodgeRamMegaCabSpecs.pdf.

Looking forward to your comments and thoughts!

Moses

connercop · November 8, 2014

To clarify, Moses, I have the 6 speed manual transmission. My truck is a 2WD and a short bed. I would guess with all of the combinations out there, mine would net just about the best fuel mileage possible. I probably tow the 11,000 Lb. trailer more than I drive the truck empty as I don't use this vehicle much unless I am towing the trailer. Where exactly is the tag on the differential that indicates the gear ratio? Also, I read on a forum (somewhere) that a 2006 with a six speed manual transmission ONLY came with 3.73 gears, however, I am sure about the RPM range as when I attempted to set the cruise by the tachometer at 2000 RPM I was closer to 60 than 65 MPH.

Moses Ludel · November 8, 2014

Connercop...In the PDF I provided on the 2006 Ram models, I also found that there is only a listing for the 3.73 gears with the 6-speed NV5600 transmission. Your rpm at 60-65 mph in overdrive (6th gear) would indicate otherwise. Here is the NV5600 ratio data for the 2006 models from the PDF linked above:

TRANSMISSION: NV5600—MANUAL, SIX-SPEED OVERDRIVE

Availability____________________________________Std. with 5.9-liter high-output diesel engine

Description_________________________________________________Synchronized in all gears

Gear Ratios

1st_______________________________________________________________________3.21

2nd______________________________________________________________________1.83

3rd______________________________________________________________________1.41

4th_______________________________________________________________________1.00

5th_______________________________________________________________________0.82

6th_______________________________________________________________________0.63

Reverse__________________________________________________________________4.44

Overall Top Gear Ratio_________________________2.72 with 3.73 axle; 2.99 with 4.10 axle ratio

Note that the final drive ratio is a 2.72:1 equivalent in 6th gear overdrive with the 3.73 axle. With 4.10:1, the final drive ratio equivalent in overdrive (6th) is 2.99:1. Your tires should be in the 31.4" to 31.6" diameter range depending upon wheel rim width and tire manufacturer. Let's use 31.5" as a baseline. At 65 mph, this translates to 1886 rpm for the 3.73 ratio axle in 6th gear and 2073 rpm for 4.10:1 axle gearing in 6th gear. There is a distinct difference. Your data for 65 mph (speedometer presumed accurate), with the corrected tach rpm, is clearly the 4.10:1 axle.

You can very simply determine the rear axle ratio with the vehicle's rear axle and tires perched safely off the ground. Mark a tire and the driveshaft position with chalk. Rotate both wheels simultaneously one exact revolution forward while counting the driveshaft rotations. You need to rotate the wheels together in order to cancel the differential's effect. (Sometimes this will occur naturally if you have a limited slip axle.) This is the actual ring gear rotation. The pinion shaft will multiply the number of rotations based upon the ring-and-pinion gear tooth counts. If the driveshaft rotates 3.73 times, you have 3.73 gears. If the driveshaft rotates 4.10 times, you have 4.10 gears.

Another way to do this is with the differential cover removed, like when you're changing the lube with the wheels off the ground. Mark the ring gear or tone ring and rotate it exactly one rotation while counting the pinion shaft/driveshaft rotations. You'll once again be looking for either 3.73 or 4.10 rotations of the pinion shaft/driveshaft to one rotation of the ring gear.

Moses

connercop · November 9, 2014

Moses,

Thanks for the info. I have counted the teeth on ring and pinion sets many times to determine ratios. Mostly for race car applications when the gear set is on the bench and not yet installed in the vehicle. I will attempt the drive shaft rotation procedure you described. I will also use a stopwatch and the mile markers to ensure the speedometer is accurate. My tires are Cooper brand and what is printed on the door sticker matches what is printed on the tire. Since I use this vehicle almost exclusively for towing, I suppose that 4.10 gears may not be the worst thing for my particular application. I considered taller tires the next time I replace them, but that may not be the best choice. I have yet to watch the video, but it sounds like that "tune" may be the way to go. I was just curious after reading your information regarding RPM and fuel mileage. I'll keep you posted.

P.S. I plan to tow the trailer at 65 MPH, which, as you noted above, puts me in the 2100 RPM range.

Moses Ludel · November 11, 2014

Connercop...I purposely geared the Ram 3500 to reach 2000-2100 rpm at 65-69 mph highway speeds. The "new" torque peak rpm (2100) with the Max Energy program is in step with maximizing fuel efficiency at the torque peak. In my case, 65 mph is 1980 rpm, 2100 is close to 69. This is with 34.6" diameter tires and 4.56:1 gearing.

In addition to mileage, my aim is to see 500K or more trouble free miles out of this Cummins 5.9L and squeeze as many miles out of the 48RE as possible before I personally pull it and do the rebuild. (When the transmission needs rebuilding, I have a list of Sonnax upgrade parts planned to extend its life for the next go-around.) The way I drive and tow, the 48RE is still quite viable at over 140K miles. I did tow your gross vehicle combination weight for about 600 miles total, several round trips during a shop equipment move. The route included an 8 percent grade with a standing start at its base, which we did five times...and the 48RE has survived to this point.

What I have learned is our trucks' sensitivity to weight, gearing and engine speed. I just returned from the Las Vegas SEMA Show. For those familiar with US. Highway 95 from Fallon, Nevada to Las Vegas, this is a peculiar road, and I'm sure you have them in your area as well. There is gradual climbing to Tonopah/Goldfield (the first 200 miles from Fernley). Goldfield is 6,100 feet, and Las Vegas is 2,184 feet, with 184.2 miles between these points. I ran the Ram with only auxiliary fuel, my unladen weight approaching 9,000 pounds with full fuel. Downhill for much of the 410 miles from Fernley to Las Vegas got me a whopping 24 miles per gallon! I only used 17 gallons over this section. On the return trip, same route, I used the 17 gallons to reach Beatty, only 120 miles from Las Vegas. The whole trip averaged 20.4 miles per gallon.

The moral of this story is that load and weight make a dramatic difference in mileage. In my experiences, loads decrease mileage far more than downgrades tend to increase mileage. I knew that when I added accessories, a lift and oversized tires, plus auxiliary fuel capacity, that the mileage would suffer. And it has. The direct gearing correction for the oversized tires would have been 4.10:1 when compared to the original 3.73 gearing. I will say with certainty that 4.10s would not have restored fuel efficiency and more than likely would have the 48RE on my workbench by now. Today, AAM offers 4.30:1 gearing (not available when I changed gears), and this might be worth a try. Or like your plan, I could try to squeeze larger tires under the fenders, perhaps a true 36" diameter. In the long run, that might be a better gamble, as we can restore tire size more readily than changing ring-and-pinion gear sets.

In earlier discussions, I mentioned the Gear Vendors overdrive as another option. You have a very busy setup with the six-speed manual transmission already, and perhaps the Gear Vendors overdrive would complicate this further. The entire premise is maximizing engine torque through split shifting, finding just the right gear for each occasion and load. To understand this premise more thoroughly, I suggest looking at the Gear Vendors approach: https://www.gearvendors.com/4x4dmanual.html. The charts confirm the sensitivity of gearing and its relationship to torque and horsepower. You can see how dramatically a subtle change will impact the balance.

When I installed the Hypertech Max Energy program with the highest output setting, the manufacturer was certain that there would be a substantial mileage gain from this single change. Unfortunately, to make that comparison would have taken me back to the stone stock truck, with no accessories, stock gearing and OE tire diameter. I made all of the current modifications before trying the Max Energy programming. If you do make this upgrade with no other changes to your Ram truck, please share the gains! This would be valuable to others considering the software program re-tune.

Moses

Megatron · November 11, 2014

TaylynQuay, like Moses said welcome to the forum.

I know Moses posted a good link that covers everything from gearing to power curve of the Cummins. It has since turned into a lengthily read but all of it is great knowledge to have.

Your question is about gaining fuel mileage. One thing I must point out is that with your setup (lift, tires etc.), like me, you really are just tying to get back to the mpg you lost in stock form. I have the 06 3500 Mega and my father has the same. He has more mileage on his but his is 100% factory with factory spec tires. His truck is control group for basing my modifications and the effect they have.

To start, I jumped straight to the 8" lift, 20x12 wheels, (now) 38"x15.50 tires, bumpers and everything. Around 9-10k# on the scales. I left the engine stock at first. Well this dropped me down to around 10-12 mpg while my father stayed in the 20-23 range... So like you the quest to improve my situation was on or should I say gain back what I lost

Now Moses points out that gearing is a thing key but the effects of gearing really (in my opinion) are just to get your cruise speeds back into the desired RPM range. This is were your engine is most efficient. Well gearing is one of the last things I planned for upgrades (mainly its something I felt I had to outsource the labor on until I read Moses's awesome post on gear installs. Now its back on for a DIY project, just not right now lol). My attention was on bolt on and tune capabilities.

So with the standard run down of aftermarket parts I began my quest. First on deck was air in and air out theory. Magnaflow 5" turbo back exhaust with a S&B intake and filter. Now most will argue that 5" is overkill, well it is.. but 4" to 5" had no ill effect either. So 5" it was lol. What I'm a guy I like bragging rights ha-ha. Well this combo did gain some increase. Maybe 1 mpg on the average. But sound was better for me and the power increase was slightly noticeable. I say win..

Next was intake S&B elbow, grid heater delete and GDP raised intake plenum. Now with these items you start crossing a line of simple modification parts to performance/dependability altering. For instance the grid heater delete. Did I gain anything or did I loose something?? The trio landed me about another .5-.75 mpg but now anytime its below 30 out I have to plug my truck in. Did I feel a power increase through the midrange?? A slight notice but nothing to brag about. Plus maybe its in my head that it was more power lol.

After that came an AirDog 2 165 lift pump and water air separator. It really didn't show up on mpg or performance scale but it did give me better filtration and rights to some neat theory's on air in the fuel. Its more of a maintenance thing.

Next was a tuner. Now the market for these things is off the chart. You can research them for days and read claims of this and that plus you can find countless haters of every type. That being said I went with EFI Live. Its not a typical tuner but it has similar results. I say better. This tuner allowed me to install a 5 way switch and have 5 tunes on the fly. Stock, MPG, Towing, Street and Performance. This modification is where my MPG saw the biggest increase.

Now you would think that Stock or MPG tunes would offer the best for MPG well that turns out to be incorrect on my truck. When set to performance I saw the biggest increase of mpg and power out of any previous modification. It jumped me up to around 19-20 mpg. Why you ask?? same question I had.. I think with the miss-match of tire size and gearing in my truck the rpm range is out of alignment with cruising speeds. This is the only explanation I can think of that ties a power increase to a mpg increase. By increasing my power curve through fuel delivery and timing I managed to encompass the rpm range of my cruising speed. This resulted in better fuel efficiency. At anytime if I switch to any other tune or even tunes from different tuners the results are the same. I lose power and mpg.

Now keep in mind my power tunes are not crazy coal rolling with transmission breaking torque. I don't support the Coal Rollers of America. To me power can be made cleanly and should be. The fact remains that everything Moses has showed us is that its all about the engine being at its efficient range for power. If you can mange to operate your vehicle in this window you will regain lost mpg. I have never reached back to the stock level that my father has, and he reminds me every time I see him lol. But I have started to get a more respectful number in the MPG game. I have a few more things sitting on the shop floor right now that I hope will lead me back closer to the stock mpg.

To add, making power with the Cummins engine is easy and when done with respect you can gain mpg with that extra power. The question I want to know is that if I put the rest of my truck back to stock (height and stance) where would my mpg's be then?? Would I have increased it or not? I wont ever know because I love lifted trucks ha-ha. To me all these add on's are just trying to recoup what I lost but I'm not really for sure how far a stock truck could go. I have seen claims up to 30mpg on a stock truck but I have never seen it with my own eyes.

Also, driving style plays a huge factor in mpg. That's a big one. Easy on the on ramps, easy off the green lights etc. Staying around that rpm range that your engine likes.

KeriOkie · November 12, 2014

Hi. We just bought a 2004 Dodge 3500 Cummins 4x4 today w/only 31,700 miles on it. Everything is stock. I'm really enjoying reading this thread. It's a lot to take in at once, so I'll digest a little at a time and I'm sure I'll have questions. Here is our truck, it's still on the dealership web-site right now. http://www.rochestertoyota.net/car/244989/2004_Dodge_Ram_3500_SLT?lpid=97 Does anybody have any suggestions right off? We want to make this truck last a long time.

Thanks,

Keri

biggman100 · November 12, 2014

Megatron, just a thought. You said you want to know how much of an increase you would get if your truck was stock, with the EFI live tuner. One idea, if your dad has the same truck, but his is all stock, would be to plug your tuner in to his truck, and see what changes it makes, good or bad. The downside, of course, would be that he sees a major improvement and then wants to keep the tuner. Also, once you see how his is on the tuner, you might not like yours as much.

Megatron · November 12, 2014

My old man wont let me in 50' of his truck with any of my new fangled hot rod parts ha-ha-ha. I have tried to do so. I figured with his grandpa style driving we could get 30+mpg out of his truck but his reply is always "If the factory wanted it on there, they would have put it on there" lol.. He is the perfect test subject but old school is old school.. Probably goes to show that he has never had to put a new transmission in or replace anything but tires lol.. Me on the other hand, I could have bought another truck just with the money in parts...

biggman100 · November 12, 2014

That sounds like my dad with his newer vehicles. But, my dad also has older trucks he drives like he is qualifying for a nascar race. And i know how you feel about how much you have spent on parts. With what i have spent on the last 5 Dakotas, and the last 3 Subarus, i probably could have bought 3 new Subarus.

Moses Ludel · November 13, 2014

Wow, very low mileage on this one, KeriOkie! For a Cummins Ram truck, this is a great find, barely broken-in! I looked at the pics. Other than color, you have essentially the same truck we bought new as an '05 model ten years ago.

If the truck is bone stock and you're after mileage, your "new" Ram 3500 is in the best form it will ever be. With the 48RE automatic and 3.73 axle gearing, if you run the engine between 1600 and 1900 rpm, you will gain maximum fuel efficiency. As others like Megatron note, don't do heavy throttle dead starts or hold the transmission in lower gears under high rpm sprints. Running empty, using mild throttle at this rpm range can yield 23-24 mpg if that's your aim.

I have recommended engine tune reprogramming for modified and weightier models that have already gone over the cliff with fuel efficiency losses. For stone stock gearing, stock tire size, no lift or colossal add-ons, Chrysler had this truck dialed for fuel efficiency in stock form. Yes, the Hypertech 'Max Energy' programmer bumps up horsepower and torque but at a higher rpm (2100 rpm torque peak instead of 1600). If you experiment with this approach, there is a high, mild and stock performance setting. Megatron talks about a programmer that has push-button settings, which would be handier than the software "reprogramming" necessary to change modes with the Hypertech setup.

Try driving the truck as-is and enjoy it for a bit before considering any modifications or changes. Assuming it has stock engine programming now, you're in business for power and fuel efficiency within the 1600-1900 rpm range. For fuel efficiency, the closer to 1600 rpm, the better! My very best mileage when stone stock without a load was 25 mpg, done over a 500-plus mile test (Reno, Nevada to Portland, Oregon) with varied road and load conditions, driving mostly between 1600-1800 rpm.

All of us need to keep in mind that extracting latent horsepower and torque from a turbo-diesel like the ISB Cummins comes at a price: heat and fuel consumption. If we boost horsepower or torque and stay in the throttle to realize these gains under severe loads, the result is engine-killing heat and huge losses in fuel efficiency. If you intend to push an ISB Cummins diesel, I heartily recommend a pyrometer, installed pre-turbo in the exhaust manifold (without leaving drill or tap debris in the manifold!) to monitor maximum exhaust manifold temperatures! Apply less right foot pressure to lower temperatures.

Keep us posted on this gem of a find!

Moses

smokes3456 · December 16, 2014

I have an 06 3500 manual transmission DRW. according to the build sheet it has 3.73:1 gears and at 55 I'm turning roughly 1725 rpm. I am able to maintain about 24.5 to 26 MPGs empty and 11-16 loaded. I am looking to bump my torque range up a little bit. I drive commercially and tow varying weights and trailer configurations about 50-60% of my drive time. I am looking at Banks to get all mods from the same place to ensure everything works together as it should. Where should I start? Exhaust and intake first or tuner? Pyrometer and boost gauge will be installed prior to purchasing a tuner.

smokes3456 · December 16, 2014

I should add it's a 2wd crew cab (not the megacab) LWB on 235/80 17 firestone transforce tires on stock rims inflated to 60 psi.

Moses Ludel · December 16, 2014

Smokes3456...I did the Hypertech Max Energy program for exactly the reason you want: peak torque at a higher rpm. Take a look at my article on the magazine site and see the results. This is the only modification I've made. There are many more (i.e., costly) solutions and upgrades, this was my simpler initial approach:

http://www.4wdmechanix.com/Hypertech-Max-Energy-Power-Programmers-for-Jeep-4.0L-and-Dodge-Cummins.html

After reviewing the torque gains and my comments, let's pick this up again...

Moses

smokes3456 · December 16, 2014

I must say this has been the most informative post I have found to date. I have an 06 3500 manual transmission DRW. according to the build sheet it has 3.73:1 gears and at 55 I'm turning roughly 1725 rpm. I am able to maintain about 24.5 to 26 MPGs empty and 11-16 loaded. I am looking to bump my torque range up a little bit. I drive commercially and tow varying weights and trailer configurations about 50-60% of my drive time. I am looking at Banks to get all mods from the same place to ensure everything works together as it should. Where should I start? Exhaust and intake first or tuner? Pyrometer and boost gauge will be installed prior to purchasing a tuner. I should add it's a 2wd crew cab (not the megacab) LWB on 235/80 17 firestone transforce tires on stock rims inflated to 60 psi.

smokes3456 · December 16, 2014

Sorry, my phone kept telling me the original posts didn't happen

smokes3456 · December 17, 2014

So if I have this right the hypertext tuner brought your peak torque up to around 2100 rpm. Understanding that higher rpm means more fuel being pushed into the motor that would lead me to believe that my fuel mileage May drop off some. Is this true or is the change in injector timing enough of a change to use the same amount of fuel at 2100 as it is currently using @ 1600?

Moses Ludel · December 18, 2014

You're very correct in your assumptions, smokes3456! I've shared that when we make any of these changes or upgrades, there should be a purpose. To be technical, you will actually get better fuel efficiency at 2,100 rpm with the Hypertech solution than with your stock tuning program at that same 2,100 rpm.

Here's the reasoning: If the stock torque peak (currently 1600 rpm on your HO 5.9L) begins to drop by 2,100 rpm, then the engine is not as efficient as it could be at that rpm. The program I installed not only raises the torque peak rpm, it also increases the torque output at that rpm. So I'm gaining both additional torque and the ability to operate the engine at a higher rpm. This higher rpm is desirable when I'm not towing. I've actually geared the truck for the "discipline" of towing at 65 mph, which is 1980 rpm with the current gearing (4.56) and tire diameter (around 584 revs/mile). When not towing, however, I do want to go 69 or 70 mph, the posted local interstate speed. My current engine rpm at these speeds is approximately 2100-2150 rpm.

Note: Often overlooked with tire and wheel changes is the inaccuracy of the revs/mile. My BFG All-Terrain tires have an advertised revs/mile of 601. On the 9" aftermarket rims, to get my speedometer correct, I had to factor 584 revs/mile. This tire, though called a 35" (really 34.6" at 601 rpm), is actually stretching to 35.5" on this rim. Next tire change, I may try a true 36.5"-37" diameter tire if the chassis lift will allow it. This would drop revs/mile to 560-568, and engine rpm would drop correspondingly. At 560 revs/mile (true 37" diameter), 69 and 70 mph would be 2,026 and 2056 rpm.

There's no free lunch. We're striving for optimal fuel efficiency for an intended or desired road speed and engine rpm. In my experience, maximum fuel efficiency is always around the torque peak rpm. As a footnote on this, Cummins actually wants to see a commercial truck with this 5.9L ISB engine spinning 2100 to 2400 rpm for best economy and performance. This begs the question: What is the tuning program in these commercial 5.9L ISB applications that can lug up to 50K gross vehicle weight? My guess is that the tuning would be very close to the Hypertech Max Energy program, which Hypertech indicates is "tow friendly".

Regardless of engine tune, the pyrometer is a great idea. Pulling more horsepower out of a diesel engine, whether stone stock tune or built for tractor pulls, is always a matter of shoving more fuel into the engine. And this results in a heat rise. Heat can damage, and using a pyrometer is just as important as watching the tachometer!

I plan to install a pyrometer before we begin trailer towing on a regular basis. Our 5.9L is now "just broken-in" at 140K conservative load miles. Only 12,000 or so miles have been trailer pulling, and I am considerate of the powertrain when towing. (I do have a pyrometer of sorts: My heavy equipment operating background governs the pressure at my throttle foot.) I plan for this truck to last a very long time, even with the increased piston travel I created with the lower (numerically higher) axle gearing. Despite that increased piston travel, the gearing does decrease load on the engine. As I noted, a good compromise or "rpm tune" would be 36.5" or even 37" (true to size) tires to get the rpm down some with these 4.56 axle gears...Otherwise, 4.30:1 gearing would be optimal with the current tire diameter.

For your purposes, I would share that the best fuel efficiency I ever got was stock and with 3.73 gears, using the 0.69 overdrive in the 48RE automatic transmission, and running stock wheels and tires. That was between 65-69 mph, the tip-over point was 70, after which I would "pay for the privilege" of driving faster and using more fuel. Hypertech told me that fuel efficiency goes up with its programming, and this might be a worthwhile gamble; the torque even increases at the stock torque peak of 1,600 rpm and continues to increase to 2,100 rpm. See the dyne chart at the magazine article...

Your current fuel efficiency is a true credit to your driving technique. I cannot imagine any modification that would get you better than 26 mpg. Even the 24.5 mpg is excellent. There are some with our trucks who cannot muster 20 mpg stock, and this can only be due to driving technique. When stock, my truck's peak mileage was consistent with yours, and the truck is an SRW with a Quad Cab, likely lighter than your DRW truck.

Moses

smokes3456 · December 28, 2014

Thanks for the kind words Moses. This truck gets the credit for teaching me how to drive. I spent my younger years in the hot rod train of thought...the faster the better never mind fuel costs. Driving for profit and watching the fuel needle drop quickly the first couple trips out got me to thinking about economy. Now my acceleration happens as though there is an egg under the pedal and I don't want to break it (I routinely get out run by 18wheelers when leaving red lights). Coming to a stop happens almost as slowly and using these techniques have helped as much as watching the tach. Now that Christmas is over I did manage to set a little money back and am installing a 100 gallon tank in my bed tomorrow. My hope is that finding cheap fuel and buying bulk will be able to help me save the cash for future upgrades.

I apologize for the delay in responding...with 4 kids and a flock of nieces and nephews Christmas is a whirlwind for us.

Moses Ludel · December 28, 2014

Sounds like Christmas was fun, smokes3456! I had to smile about the "egg under the pedal" comment, that was my father's mantra when teaching me to drive the four-cylinder Jeep CJ-5 with a T98 four-speed transmission. Fuel was cheap but he had lived through the Great Depression Era...It was the Muscle Car Era at the time, and acceleration was the order of the day with Nevada's "basic speed law" in the 'sixties. Essentially, there was no speed limit in rural areas if traffic was light and the pavement dry.

Since the mid- 'nineties, after many years of testing performance cars like the ZR-1 Corvette for magazines, my driving technique has been like yours. When unloaded, the upshifts with the Ram 3500 diesel and 48RE transmission have averaged around 1350 rpm (1200-1500 rpm) since new. This is how you get fuel efficiency with any engine and especially a truck design diesel. We are so fortunate to have Cummins power in our light trucks—drive accordingly!

The 100 gallon tank will do the trick. I have a 75 gallon Transfer Flow tank plus the factory 34 gallon tank. This is really the ticket for long trips. I fill at our town, Fernley, Nevada, one of the least expensive fuel sites in the West and along I-80. (When the price is competitive, I fill with GDiesel at Sparks, Nevada. I prefer using GDiesel over any other diesel fuel or additive. See my article and video at: http://www.4wdmechanix.com/Performance-Diesel-Fuel-GDiesel.html.) Here are some details on my tank and Transfer Flow:

http://www.4wdmechanix.com/HD-Video-Transfer-Flow-Fuel-Tank-Manufacturing-Process.html, http://www.4wdmechanix.com/Dodge-Ram-3500-Makeover-Transfer-Flow-Auxiliary-Fuel-Tank.html, and http://www.4wdmechanix.com/2005-Dodge-Ram-3500-Major-Makeover.html

I can drive to Moab, Utah and back (about 720 miles each way) with plenty of fuel left over, passing all of the stations en route and back, avoiding the higher priced fuel. SEMA Show Las Vegas, the round trip is simple with plenty left over. San Diego, the Pacific Northwest, it's all on Fernley or Sparks fuel! California is definitely the state to avoid fuel purchases. On rare occasions, like when pulling a travel trailer, I will top off fuel at Independence, California, the tribal owned station with discount diesel fuel.

Which tank did you get? We'd like to see photos of the install. You're going to really enjoy this tank and fuel range! Expect a slight drop in mileage with the added weight when the auxiliary tank is full, that's 850-900 pounds of add-on tank and fuel weight depending upon the new tank's weight. Worth the trade-off.

Moses

smokes3456 · January 12, 2015

Hi Moses, sorry I've been busy helping my parents get ready to move so I haven't been on in a while. I purchased a better built 100 gal tank and have it bolted in but am working on a way to plumb it into the factory fuel tank. I am going to run a T into the filler neck but am having an issue with getting fuel out of the tank without spending another $300 on the pump that mounts to the top of the tank. Those pumps are an eyesore to me and I need another solution that will allow me to pump fuel while driving. It is a steel tank and I have thought about going to a shop and having them weld a fitting to the bottom corner of the tank...just have to make the time.

Moses Ludel · January 12, 2015

smokes3456...I have a Transfer Flow tank with its own pump and filter, plus the automatic Transfer Flow transfer system. You can see the complete installation at my magazine article and videos: http://www.4wdmechanix.com/Dodge-Ram-3500-Makeover-Transfer-Flow-Auxiliary-Fuel-Tank.html. This may prompt some ideas or furnish a source for parts if Transfer Flow will sell separate components.

Check out the article and videos for details...We'll go from there.

Moses

smokes3456 · January 13, 2015

I looked into the transfer flow line of products but decided the convience wasn't worth that large of a price tag, especially knowing that some of the other guys I pull with have installed a "automatic" fuel system in their trucks. A fair # of guys are running a gravity feed system with a manual shut off valve operated by a couple of bicycle brake cables from inside the truck. Looks...interesting but it works(probably not something that would look like it belongs on a truck at the SEMA show.)

Moses Ludel · January 13, 2015

I applaud ingenuity. On the other hand, if you do any kind of manual valve and splicing into the current fuel supply lines, keep in mind that your '04 system's fuel supply lines to the engine are highly pressurized by the in-tank pump!

I'm guessing that manual valves get tapped into the system above the fuel tank at the fuel filler overflow/return hose or some such unpressurized point...Earlier Ram/Cummins systems use a fuel pump at the engine. Our chassis uses an electric, in-tank pump, a nice feature for priming the system when the tank runs dry or during service...

Get a diagram of a commercial fuel supply system that uses a manual valve with an auxiliary tank—know where to install the auxiliary tank's gravity feed supply line. The Transfer Flow tank uses its own in-tank fuel pump to pump fuel out of the Transfer Flow tank, through an inexpensive replaceable filter, and into the Ram truck's OE tank.

Moses

smokes3456 · January 14, 2015

Yes these guys are running the fuel into the factory tank by way of a T fitting in the filler neck. One guy I know has run a solenoid valve into the engine feed line. When the factory tank is near empty he flips a switch and runs off the aux tank for a while, the fuel return line puts the unused fuel into the factory tank. When the factory tank is full he flips back to it. Sounds like a pain to keep up with, having to keep that close an eye on the fuel gauge for so long but whatever works for him. I should add that he is driving a "Driver Returns On Foot" so there must still be a mechanical pump under the hood. I will be talking to a friend who is using a tank like mine in a couple days, I'm going to find out how he is handling this issue.

jimbopa · February 15, 2015

Found this site via a Google search & read quite a few threads. Like many of the participants here, I am looking for the best fuel efficiency I can coax from the 2006 Dodge Ram 2500 4 x 4 Off Road I purchased last summer. Originally, I had a 07 Jeep GC with the 3.0 CRD Mercedes model. I used the Jeep as a personal vehicle & to tow a small utility trailer GVW 3000 lbs. Last summer I purchased a Lance TT that had a loaded wt of just over 5,000 lbs & tongue weight of approximately 650 lbs. On a trip from PA to TN, GA, VA the Jeep did a nice job of towing & delivering approximately 14 mpg. On the second half of the trip the Jeep began to throw a 4 wheel drive system "needs service" code. After the first Jeep dealer in NC found nothing to fix & basically turned of the code the code again activated & the vehicle had to be towed from a campground to a second Jeep dealer. The issue turned out to be a minor part: front diff actuator for ther Quadra Drive II system.

Since we were planning more extended TT towing to mountain regions in CO, WY, etc , I decided to move to a more robust tow vehicle: thus the 2006 one owner FLA registered Dodge Ram 2500, 4 x 4 with 112k. The truck runs great, has good service history and looks to be well cared for. It is equipped with the "legendary" 5.9 HO Cummins Turbo diesel, 48RE 4-Spd Auto Trans & 4.10 Axle Ratio with towing package. It is a Laramie Quad Cab, 6.5' bed, running LT265/70R17E all season tires. I had new DynaTrac Ball Joints installed which, after a little sticky break in period, are tracking very well.

Initially I was relying on the vehicle trip computer for mpg figures. On rural back country PA roads with little stop and go and very conservative driving I would see 24 - 26 mpg figures reported by the vehicle computer. My computer on the 07 Jeep had always UNDER REPORTED mpg by about 2 mpg, so I was very happy. It looked like towing the trailer was providing 15 - 17 mpg depending on the terrain. HOWEVER, MY FREQUENT FUEL STOPS LED ME TO BELIEVE SOMETHING WAS A BIT OFF! TRY THE TRIP COMPUTER OVER REPORTING MPG WITH ERRORS RANGING FROM 5 TO 9 MPG.

Looks like my fuel economy basically SUCKS! Try about 15 mpg non towing rural driving & 11 mpg towing the 5,000 lb Lance Travel Trailer. While I can't imagine diving too deeply into the "sweet spot" rpm theory (sounds reasonable & well informed) I am driving with a "light foot" & have achieved excellent results with every other vehicle I have owned. I did replace the well cared for K & N air filter & may have noticed a little difference, but I'm at a loss to see how some of you folks are achieving the 23 to 25 mpg averages with a heavier 3500 Ram dually. ANY IDEAS???

Moses Ludel · February 16, 2015

Hi, Jimbopa, welcome to the forums! I read your post with great interest, as your truck is essential the same as mine was when it was stock. Everything matches up except the gearing: I had 3.73:1 with stock tire size when the 25 mpg peak was achieved. Average at cruise on flat ground was consistently 22-23 mpg in the 1600-1900 engine rpm range. This was without a load.

Use the actual fill-up and mileage tracking method for determining fuel efficiency. The computer can be nebulous, though mine was accurate when everything was stock. The VIN on your truck will share whether the rear axle ratio is original, and it could be, though 3.73 was common on SRW trucks. Your 2500 is not a dually. 4.10 gearing was optional.

If the comparison is accurate, the 4.10 gears could make a difference in fuel efficiency. When I went to 35" tires, the precise correction for the speedometer would have been 4.10 from the original 3.73. I can share that my mileage today would be better with 4.10 than the 4.56 alternative path that I took.

Since you're pulling the trailer, I would think 4.10 is a wise choice, and any increase in tire diameter requires a chassis lift. (My truck has a 4" lift for the 35" tires.) Unless a lift is your plan, you have the option of 3.73 gears, which from my experience would get around 17 mpg with the 5K pound trailer in tow. Is that worth it? The 4.10 gears are actually a bit lower (numerically higher) than I'd want for running the truck without a load.

Before considering a gearing change or lift and oversized tires, check the speedometer accuracy and run the fill-up to fill-up mileage test without the onboard computer. Try the back roads and 1600-1900 rpm engine speed if possible. Share your mileage at that point, we'll discuss this further.

Moses

smokes3456 · February 16, 2015

Jimpoba, the major difference is in the gearing. While 3.73 gearing is good for the milage number climbing hills loaded is not my trucks strong point. Most climbs I am able to maintain speed but on some of the steepest climbs in TN and KY I will either overheat my turbo(high EGT) or lose speed. If milage is what you are after I would look seriously at a Gear Vender's overdrive unit, although Gear Vender says not to use the overdrive in high gear when loaded(that's what they said for my truck anyway which is why I have not gone that route, with the 4.10 gearing yours may be different).

Moses Ludel · February 17, 2015

smokes3456...I have suggested the Gear Vendors in other replies, nobody has tried one yet. On paper, it does look like the best solution, though somewhat costly to amortize. I've considered a Gear Vendors overdrive, especially with the limitations of the 48RE four-speed automatic and 4.56:1 gearing.

Thanks for bringing this up. I believe you're right about 3.73s and overloading. 4.10s are more forgiving when trailer pulling. My 4.56s with 34.5" tires (new 35x12.50x18 BFG All-Terrain T/A KO2 type) pull very nicely when trailer weight is involved.

Moses

Driving Your Dodge Ram Cummins for Fuel Efficiency!

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