I have a 1998 4.2L single cab standard which will overheat at any speed over 60 mph. under that speed it regulates temp fine. if i turn it off at freeway speed and then start it back up a couple seconds later, it drops back to operating temp. I have changed the thermostat twice, cant find any water or coolant in the oil, I AM STUMPED!!! Any help is much appreciated.

 

http://www.aa1car.com/library/overheat.htm

 

After it starts running hot, is there a loss of coolant (not talking about boil-over)?

First thoughts are it is getting into combustion chamber and being blown out the tailpipe, but it would most likely smoke, or cylinder pressure could be entering the cooling system which would push out coolant without necessarily putting oil in the cooling system, I think they sell a test kit to see if there is any hydrocarbons present in the coolant... I had that issue with a turbo setup on a Mustang, just fine normally, but under boost, with a head gasket on the way out it would bleed pressure into the cooling system and push out the coolant, normal driving conditions it was fine...

Another thought, at a higher & steady rpm, I wonder if there is a cavitation issue in the water pump?

 

Jeez, what a huge help.

I guess you didn't read all the stuff he's tried already.

I'm having the same problem.

The truck ISN'T ACTUALLY OVERHEATING.

I wonder if ANYBODY knows how to fix it.