I found this forum with a Google search. I hope you can help me out. I have a 94 GMC that's acting weird on me . As I'm driving it temp gauge fluxes on me it tells me at times it's at 160 degrees the jumps into the red zone out of nowhere. Wait it"s not over. When the temp hits the red zone the check engine and check gauges light comes on but goes off when the temps go down. Weird but there's more. When i come to a stop the temp seams to go down not up and when i start driving the temp fluxes back and forth again. Also the heater goes weird on me to . Out of nowhere it blows cold air then blows hot and back and forth /w the temp changes. Now when I got home I pop'd the hood and the top radiator hose was cold to the touch. I'm baffled . . . . i hopn someone knows .....

 

i just went through the exact same thing on my 93. turned out to be 2 problems, bad thermostat and bad antifreeze. both very easy fixes and cheap, i'd start with the thermostat, which is cheap ($15), follow the top hose out of the radiator and disconnect it at the top of the engine at the thermostat housing. you will spill some antifreeze. just simply pop out the old one out and put the new one in, i'd also change the gasket out as well since they are only like $1.

good luck

 

thanks for the heads up . . I'll check it out & replace .... It's simple enough to do.. . . . It's getting cold quick up here in Portland so i want to fix this asap.

 

im up in canada and it was -40 celsius with windchill a few weeks and the thermostat went and the antifreeze froze