7.3 IDI overheating issue!!

[GateKeeper]

Hello all! Im new to the forums and diesel trucks in general. What i have is a 1993 Fsuper duty with the 7.3 dually truck with 168,000Km. Everything on the truck works fine except once im up on the highway either loaded or unloaded it doesnt matter there is a small jump in rpm (about 200 or so) and this causes my truck to start overheating! everytime it randomly jumps this small amount of rpm! Took it in to a couple of diesel shops and they didnt seem to believe me about the rpm jump happening.

Any info on this would be much appreciated, hopefully someone has solved this before.

 

[quickster]

Welcome. first of all, don't trust the gauges. Does the temp light come on? I was just reading about someone else having sortof the same issue. "There are two coolant temp sensors on these engines. One is for the gauge, the second is for the dummy light. If the dummy light trips, it pegs the gauge as well to try and really get the attention of the idiot driver before something worse happens". Outside of the gauges, have you replaced the t stat? Use a Motorcraft one. I don't think the fan clutch would cause that scenario, but I'm sure someone else will chime in.

 

[GateKeeper]

Hey! Thanks for the reply quickster. The thermostat has been changed and the truck also has a newer radiator installed on it as well. I always keep a close eye on my gauges out of habit. Dummy light did not come on.

 

[snicklas]

Is this truck an automatic? The 200 RPM jump to me sounds like the torque converter unlocking or slipping, causing a bunch of heat in the transmission, that is then transferred to the radiator via the transmission cooler in the bottom of the radiator. This increases the coolant temperature and raises the temp in the engine. Does your O/D OFF light work? If so, does it flash when this RPM increase occurs?