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

 

it very well could be the fan clutch. Try to spin the fan.... if it spins freely, you have a bad fan clutch. It should be very tight to turn.

It could also be your torque converter. You have a lot of miles on your truck and if it's never been dealt with..... I bet that is your problem.

 

Would a bad torque converter also raise his trans temps?

 

The transmission does make your radiator warmer in auto's don't it. and bad converter would produce more heat so...

 

The engine temp will only be warmer if the auto trans fluid lines are routed through the engine radiator. They do this to eliminate the need for a separate radiator for the transmission. But I bet your 98 has a separate radiator for transmission cooling. Look up by the radiator for a "mini" radiator, most likely in front of the engine radiator, that is anywhere from 6"x12" to 12"x24". If you have an external transmission cooler, then the torque converter is not causing your increased temps.

 

I do have an oversized tranny cooler. Trans temp light never comes on. Should I start with the fan clutch then????

Thanks
Chris

 

I thought the fan should spin freely if it was good and be tight if it had a problem? Do I have it backwards?

 

Yep, that's backwards. The clutch needs to be very tight... almost to the point you can't turn it. If it's loose, it's bad.

 

OK I'm stupid. I went out to turn my fan. I can turn the fan easily with one hand, although it does not just spin. Should I be turning the actual fan or or trying to reach down and turn the clutch itself. Duh !!. ..

Thanks
Again

 

you will be able to turn the "fan" but, it won't turn freely if it's good. It might spin a 1/4 turn by hand.

I betting the TQ is your problem though. If it's slipping, oversize cooler or not, your trans temp are going to raise.