Jump to content

Search the Community

Showing results for tags 'fuel mileage'.

  • Search By Tags

    Type tags separated by commas.
  • Search By Author

Content Type


  • Jeep® 4WD Owners Group
    • Vintage Jeep® Vehicles 1941-71
    • 1972-86 AMC/Jeep® CJ and Jeepster Models
    • Jeep® YJ Wrangler, TJ Wrangler and LJ Wrangler
    • 2007-Up Jeep® JK Wrangler 4x4
    • Jeep® XJ Cherokee, MJ Comanche Pickup and Grand Cherokee
    • FSJ Models: Full-Size Jeep® Gladiator and J-Truck, Cherokee, Wagoneer and Grand Wagoneer
    • Jeep® Liberty, Commander, Patriot and Compass
  • Dodge Power Wagon, Dodge and Ram 4WD Trucks
    • Dodge 4x4 and Ram 4WD Trucks
    • Dodge-Ram Cummins Power
    • 1941-1980: Dodge Military Trucks and Civilian W-Series Power Wagon
  • Chevrolet & GMC 4x4 Trucks and SUVs
    • Vintage to 1991: Chevrolet & GMC NAPCO and K-Model 4x4 Trucks
    • 1987-Present: Chevrolet & GMC Silverado, S-Trucks and 4x4 Suburban, Yukon and Blazer
    • Humvee and Hummer H1, H2 and H3 Forum
  • Ford 4x4 F-Series, Full-Size SUV and Ranger Trucks, Bronco II and Explorer
    • 1948-Present: Ford F-Series Trucks
    • Full-Size Ford SUV, Bronco 4x4, Excursion and Expedition
    • Ford Power Stroke Diesels
    • Ford Ranger, Bronco II, Explorer and Mercury Mountaineer
  • International-Harvester 4x4 Light Trucks, Scout and Scout II
    • International-Harvester 4x4 Light Trucks, Scout and Scout II Forum
  • Toyota Truck, Land Cruiser, FJ Cruiser, Toyota SUV and Lexus 4WD
    • Land Cruiser 4WD FJ, DJ and FJ Cruiser
    • Toyota Sequoia, Lexus, Highlander and Rav4
    • Toyota 4WD Pickup, Hi-Lux, Tacoma, Tundra and 4Runner
  • Datsun and Nissan 4x4 Trucks, Pathfinder and Xterra
    • Nissan Patrol, Pathfinder, Xterra and SUV 4x4s
    • Nissan 4WD Pickups: Datsun, Nissan, Frontier and Titan
  • 4WD Land Rover Community
    • Land Rover, Discovery & Defender 4x4s
  • 4x4 Suzuki Samurai and Sidekick/Geo Tracker
    • Suzuki 4x4 Samurai
    • Suzuki Sidekick and Geo Tracker
  • Isuzu 4x4 Pickups and SUVs
    • Isuzu 4x4 Pickups and SUVs
  • Travel Trailers, Toy Haulers, Tent Trailers and Military Surplus Trailers
    • Travel Trailer and Toy Hauler Forum
    • Military Surplus M415, M416 and Other Off-Road Trailers
    • Tent Trailers and Trailering
  • 4x4 and Single-Track Travel & Adventure Destinations!
    • Places You Have Been...
    • Places You Would Like to Travel!
    • Off-Pavement Travel Gear
    • Equipping Your 4x4 for Overland Travel
    • Health and Fitness for Four-Wheelers and Powersports Enthusiasts
  • Dirt & Dual-Sport Motorcycles
    • Dirt & Dual-Sport Motorcycles
    • Dual-Sport and Dirt Motorcycle Equipment for Overlanding
  • Quad ATV, UTV and Side-by-Side 4x4s
    • 'Quad' ATV, UTV and Side-by-Side 4x4s!
  • Welding, Metal Fabrication and Metallurgy Discussion
    • Welding and Metal Fabrication Forum
    • Metallurgy and Heat Treating Forum
  • The Right Tools and Equipment
    • Garage Tools and Equipment
    • Diagnostic and Specialty Tools & Equipment
    • Tool and Equipment Sources
  • Let's Talk and Share!
    • General Repairs and Tips (See Other Forums for Specific Vehicle Topics)
    • Off-Topic and General Discussion
    • Sharing New Products
    • Calendar Events and Outdoor Activities
  • Parts for Sale, Swap or Wanted
    • Parts for Vintage (1941-71) Jeep Vehicles
    • Parts for AMC/Jeep CJ, FSJ Cherokee, Grand Wagoneer and XJ Cherokee/Comanche
    • Parts for 1987-up Wrangler Models, Grand Cherokee and Liberty
    • Parts for 4x4 Dodge and Ram Trucks
    • Chevrolet & GMC Truck Parts
    • Parts for I-H Trucks and Scout/Scout II
    • Parts for Toyota, Nissan and Other Import 4x4 Trucks and SUV Models
    • Parts for Motorcycles, ATVs, UTVs and Snowmobiles
  • Equipment and Tools Classified Ads
    • Hand and Power Tools for Sale
    • Garage and DIY Equipment for Sale
    • Tools and Equipment Wanted


  • 2018: "Year of Speaking Out!"

Product Groups

There are no results to display.

Find results in...

Find results that contain...

Date Created

  • Start


Last Updated

  • Start


Filter by number of...


  • Start





Website URL







Found 1 result

  1. 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
  • Create New...