Hi everyone, I am new to this forum and need some help. I have a 1989 GMC Sierra with the 350 in it. I am having some overheating problems. I live near an interstate so most of my driving starts there. When I head out in the morning, before I go more than a few miles my temp gauge goes all the way to hot and the check gauges light comes on. before I can pull off the side of the road the gauge goes back down. It will do this two times and will be fine after that all day. This happens every time the truck cools off completely. If I let it idle for 5 or 10 min. before I leave I have no problem. I have replaced the thermostat twice, the temp sensor , temp switch and radiator cap. When I changed the temp switch in the head I had to put a different end on the wire, old sensor had a round button to clip the wire to but all replacements were for a spade terminal. This truck had a 165 deg. thermostat in it and I changed it to a 195 deg. because that is what it calls for. I had no problem before this.
Any help will be appreciated.

 

I need to make a correction, it is no different if I let it warm up. Pegs the gauge 2 times then it's ok.

 

Looks like this forum is not a good place to get help, glad I found a better one.

 

Sounds like a bad gauge to me. You said that you replaced the T-stat twice? Did you have an air bubble in the system?

 

Yeah, you'll need to burp the cooling system. That, or you have a bad wire in your temperature gauge. Power goes through the gauge, and grounds through the thermistor (AKA temperature switch in the head). If you unplug your temperature switch and ground it to the block, the gauge should peg. If you isolate the wire from ground, the gauge should read ice cold.

I say just burp the cooling system real good.