I just got a new radiator put into my 1990 GXL. The last one cracked right under the patent stamp. I was driving it today no problem and all of a sudden my thermostat on my dash was all the way up to H. i was like what the heck and let go of the throttle. It instantly went down again to a bit above normal running temperature. I drove it home and watched the thermostat go up and down like a rollercoaster. I let it idle at home and the engine seemed to be cool, not hot at all.

I was thinking maybe i need a new thermostat? Or any other ideas? Thanks a lot

 

it might be a bad sensor?

might as well replace the thermostat first though. they are pretty cheap. just don't buy a stant one, get the OEM replacement. Spooledupracing sells em on the forums.

 

OEM thermostat and OEM radiator cap.

 

Why is your thermostat on your dash? It can't get coolant flow there so that's probably the issue.

 

Did you bleed the system of air bubbles?

Also, if the temperature gauge wire is shorting to ground, the gauge will shoot straight up.