I have a 1997 Dodge with the 5.9 12 valve Cummings. I have a minor plate update on fuel pump, 4" turbo back MBRP exhaust, and a cold air intake. The truck has just over 100,000 miles and runs amazing, until I hook up a trailer with a heavy load (+6,000 lbs). It will haul the heavy load on the flat terian with out any problem, once I hit a mountain pass or heavy grade incline the engine temp. clime quickly to almost overheating. Using the deductive process, the following items have been replaced, thermostat, temp sending unit, clutch fan, water pump, and finally I installed an aluminum radiator, the problem still exists????? What am I missing??? I have removed the intercooler and thoroughly cleaned in-between them.

 

I am going to guess you have an automatic transmission.

I bet that is the real culprit of your overheating. You see the transmission cooler dumps lots of heat into the coolant system.
Stock transmissions with stock torque converters, slip more with the extra power you added. That coupled with the trailer load produces lots of heat.

That would be my 1st guess.

 

Yes, you are correct, so what would be my best course of action?? I have owned the truck since new and it did not have these problems early in it life. Please advise what can be done?

 

Upgrading the torque converter to work with your new found power will help cut down on slipping which will drop the temps.

I am sure other auto gurus will chime in with other upgrades you can do while the transmission is out.

I am guessing early in its life it did not have a fuel plate, hence slipping and heat where kept in check..

 

Thank you for your input, lets see what other Cummings experts think. Again, thank you!!!

 

You can always install a transmission temp sensor in the out going line out the transmission and see what temps you are running when towing.

Some first gens could be ordered with an extra air to oil cooler with a fan that cooled the transmission fluid as well as the anti freeze to ATF cooler your 2nd gen has. You could add something like that to help keep things cool.

 

That is an excellent idea that I will pursue, I do believe that you are correct in saying that the heat is coming from the transmission. The truck has always been very well cared for and all I would hate to have to replace it because of this, I really like the idea of adding the fan to cool the transmission fluid. Thanks for input and ideas!!

 

Ollie's suggestion of a temp gauge from the output line of your trans will verify the problem......Ben

 

Thanks for the advise, I will look into getting that done!!!

 

When it overheats under load, what is your engine RPM? Below 1500 it should overheat. Drop down a gear and run at least 2000 RPM for better cooling. Also, try to keep the tranny in lockup, which should occur at 44 MPH.

 

My understanding (and this comes from things I've over the years and don't remember where, plus a pretty small bit of personal experience) is that if you can't maintain OD and lockup due to frequent grade changes, it's probably better/cooler to lock out OD and just run in "3rd"/direct. This reduces the shifting back and forth between direct and OD and possibly much of the TCC locking/unlocking, which both contribute to heat.

Is your liquid/air heat-exchanger/cooler in good shape? Fins are straight and not clogged with debris? You mentioned removing the intercooler and cleaning between it and the radiator but not the condition of the IC fins - are the intercooler and AC condenser fins clear so they don't obstruct airflow to the radiator?

How heavy of a load are you towing? You said 6000+ pounds - do you have a good idea of what your load maxes out at (trailer + load)? And is your truck a 2500 or 3500?