1994 Ford F350 4x4 Engine Cooling Issues

[4x4sportsman]

94 F350 4x4 Carb engine 5.8 351w---lifted 37x12.5x16.5 tires---410 gears---c6 trans 3 speed auto----is going up to around 220 pulling boat at 50 or over-----2000 procraft 20 ft 200 hp mercury----not pulling boat its not over heating. It has got a all aluminum radiator 3 core in it-----because of lift kit had to put a 2 fan made with shroud electric cooling for the radiator---has a 180 thermostat----fans are working fine and can feel real hot air being pulled through the radiator---here's the questions I have----should I convert fans to push instead of pull because of thickness of radiator and condenser together----should I put flex fan back on it to help keep all that hot air out of bay when and if I change fans to push instead of pull---should I go another way like electric racing cooling water pump---Been advised different ways as in changing gears in rear and front axles could do the trick but that's high as I have priced it .Every things new on this motor as well as the motor--and yes I know I should be pulling boat yet till I get more miles on it less than 500 on it now---just trying to see if there's another way I can go that might help so I can keep temp down and rpm down cause if change gears it will go up.
 

[Moses Ludel]

4x4sportsman...First off, 4.10 gears with 37" diameter tires is tall gearing.  This would help with fuel efficiency (always relative with a lifted truck and weight) but would be a hindrance when towing a load.  I have a Ram/Cummins 3500 4x4 with 4.56 gears to accommodate my 37" tires.  I'm around 1980 rpm at 69 mph.  For a gasoline engine, this would be well up your torque curve though not fully there.  When towing, I try to maintain a top speed of 65 mph, which many pullers can't seem to do.  I can spin the diesel engine way beyond this speed, but fuel efficiency goes down proportionate to speed.  We both have tremendous wind resistance.  It's like pushing a billboard down the road when I tow our 30-foot travel trailer.

The radiator needs to accomplish two things:  1) dissipate the BTUs your engine produces under load with the trailer in tow, and 2) have enough volume to flow sufficient coolant through the radiator under load.  If the engine heats as rpm increases, or even starts forcing coolant out of the radiator (not overheat/boil over), that would indicate an inadequate radiator GPH flow rate.  You don't mention those symptoms.  So that leaves dissipating BTUs.  BTUs increase with horsepower demand, and BTUs are a reflection of horsepower output.

I'm not a strong advocate of electric fans.  Once the vehicle is moving at speed, fans are less relevant.  The fan(s) must not block air flow.  What you want is adequate air flow when the engine BTUs increase.  Unrestricted air flow is critical.  The amount of air flow can be helped by the correct fan when cooling demand gets high and ambient flow (without fan assistance) is not enough.  Here, a flex fan or simply a heavy duty fan clutch and heavy duty OEM steel fan will often work well. 

We had a Suburban 2500 4x4 with a 350 V-8 and A/C years ago, and I ran the OEM steel fan with a Hayden heavy duty fan clutch.  I could monitor engine heat (temp gauge) and also the air flow temperature by listening for the loud fan clutch to couple up thermostatically when radiator air flow got hot enough and the fan began to spin.  Make sure you are allowing air to flow unrestricted.  Make sure the fan(s) are adequate but not blocking air. 

Consider getting a simple "Motor Minder" or equivalent vacuum gauge to help you understand the actual engine load when the heat up occurs.  You may need the axle gearing change to get the manifold vacuum up, i.e., to relieve engine load and the need for a heavier throttle.  If you want to experiment without changing the axle gearing, borrow a set of 33" tires and see if that eliminates the cooling issue while towing.  It will run your rpm up.

Check for exhaust restrictions or other elements that impact engine heat build-up.  If load is excessive when pulling the boat, you should consider an axle gear ratio change (front and rear).  I understand that you're running a 180-degree F thermostat...Normally a 195-degree F thermostat would create a towing temp range of 195-210 F.  The thermostat doubles as a coolant restrictor.  This helps slow coolant flow through the radiator.  If coolant flows too fast, it will not dissipate enough heat.  I doubt this is the case at the towing temperatures you describe.

If your 5.8L V-8 were MFI (the original EFI), thermostat temp would be even more important.  Many late EFI systems will not come off the warm-up cycle unless a 195-degree F thermostat is used.  At 180 F, the engine can run rich.  Did you convert to a carburetor?  If so, tune can impact engine heat.  The carburetor calibration and jetting or the ignition spark advance curve (if conventional centrifugal and vacuum advance mechanisms) can raise engine temperatures under load.  What is the induction system (manifold and carburetor type), ignition type, compression ratio and tuning on this engine?  

Moses