Topic: Message #732533

[kneedownnate]

Generally, it should run cooler at higher speeds since you would have the air moving through the radiator to cool the engine. But at lower speeds the fan is needed in place of the rushing air at speed to cool the radiator.

If it runs cooler at lower speeds (less heat generated at lower RPMs and lighter loads) I might guess the fan clutch is working. Since it runs hot at higher speeds as you described, (when more heat is generated by the engine, I.E. more engine load and higher RPM) if the radiator is not efficient enough it may want to run hotter.

Is the radiator full of mud or a lot of crud like bugs, birds, small animals or children? Even heavy amounts of dirt build up will cause problems like you described. If so, you can blow out the crud with compressed air. You'll be amazed how much crap will come out of a radiator. Especially if you've spent any amount of time on dirt roads.     

Sounds like it's probably something simple. 

No offense whatsoever to anybody else, but DING DING DING!  My 2wd has a bit of crusty buildup in the radiator and runs cooler at lower speeds but runs hotter on the freeway, and even hotter towing.  My radiator is a little plugged and isn't flowing what it should, period.  If I had it rodded out I can absolute guarentee my truck would run cooler.