I have a 98 24v cummins with 238,000 miles. The truck runs fine under normal conditions. I towed my 10,000lb camper to the coast last week and the temp began to run hot after about 30 minutes. I stopped at the local auto store and replaced the thermostat. The radiator has been recently flushed also. the truck normally stays on about 190.

After getting on flat ground I put the truck in overdrive. This is when it heats up. I can push the button to go back to drive and within 20 seconds the temp guage goes from 240+ back down to about 200 degrees, the temp guage really moves back down quick. I know the truck can't possibly cool down that fast. (I think).

Any suggestions would be greatly appreciated.

I was told a fan clutch wearing out could be on possible cause.

Thanks
Chris

 

I had a old 73 chevy pick up that use to do the same thing. Found out, even with all the flushing I did, the radiator was just shot. the core needed to be rodded.. So I just wonund up buying a new one. It pretty much sounds like your having the same issue. Now if it is a new radiator, chaces are the clutch fan. Easy way to check... with the engine turned off (for the love of god, don't do this with it turned on!) stick your hand near the fan and see if it rotates on its own. I will have sone resistance, but not too much. If it takes some work to turn it, then your clutch failed and now you have a solid fan. Bad thing, it's gonna put a lot of ware on your water pump... not really good, not really too bad, the fan will always rotate.

I have seen in some rare cases where the clutch rotates too much, meaning your engine turns and the fan just sits there or spins slowly (think of those ghetto spinner rims from like AutoZone). This issue will result in the radiator not being able to cool down because there isn't enough air being pulled across the fins.

But more than likely your radiator is plugged up. If I'm wrong, just tell me I'm wrong