I am pulling my trailer and my temp was red lineing. When I turned the heat on it would maintain temp and would cool quickly when flat or down hill. I also noticed this temp rise while running just the truck, again it would cool while driving flat and downhill. Can this be thermostat whaterpump or what? any help would be great, I got to head for home soon and i got to pull some massive hills on the way home. I do not cherish the idea of being stuck on the highway.
thanks in advance...G-len

 

Your radiator is probably dirty. It is a real PAIN to get in between the fan and the intercooler to clean it. Some guys take some 1/4" copper tubing and mount it to a gadren hose. Cap the end and the cut a small slit in the bottom to make a 90* spray nozzle. Soak it good with degreaser first. When you have time, pull the radiator and steam clean it.

Usually the problem stems from the puke bottle spraying oil all over the engine side of the radiator which holds on to dirt and debris.

I had the same problem. With the same symptoms. cleared it all up for me.

The other thing it could be is if you installed an after market thermostat. The factory oem ones have a weep hole. One of the few times I suggest to get a part from the dealer.

Others will chime in as well. One thing for sure, dont go very far with you temp in the red, very bad!!!

 

As wyododge already suggested, its probably your radiator dirty with oily residue and dirt from the engine vent catch bottle located between the radiator and the front of the engine.

 

don't play around. Pull the radiator & be done. Make sure you have Cummins thermostat & not anything aftermarket.