QuestionI have a 1989 GMC Sierra truck, 4.3L,6 Cyl.It has 280,000 miles on it.After I drive it for 6 miles or so, the engine overheats.But there are no coolant leaks and it has plenty of coolant.The radiator fan is working and the belt is fine.There are no signs of a bad head gasket and the engine has plenty of power.Could tou tell me what to check out and what could be causing it to overheat? Could it be due to the very high mileage on the engine? Many thanks.
AnswerHi James,
I doubt the mileage is the problem.
First, I would like to know if it is loosing coolant,(I assume not from what you say), or how do you know it is overheating? Gauge?? could be the gauge or sender.
If you have measured, and it is above, say, 230, then the thermostat may be stuck, the water pump could for some reason not be moving coolant, the radiator tubes could be plugged inside, or the air flow could be restricted through the fins.
If an automatic transmission, it could be slipping and causing the heat.
On an 89, I am not sure if yours still has a heat riser in the exhaust manifold, old style, or not. But temperature vacuum switches for them caused me some problems several years ago.
Any major restriction in the exhaust system could cause it, like a crushed pipe, rust flakes stacking up against the holes in the muffler or spark screen in the tail pipe, or a plugged cat.
Fan clutch is another possibility, but you said it was working ok.
Good luck,
Van
