OK I got my car a few months ago and ever since I had it the temp gauge always seemed kinda high, like 220 or so. Well later I noticed that while idleing the temp would start to raise then after reaching 240-260, the thing would just jump back down to 220 again. So I figure that the thermostat was sticking. Well I replaced that with a 180 degree one, and tried testing it again. Well same problem still exsists. Now I noticed a few things since then. First, only one of my front fans works (this wouldn't cause the jumping though) and second on the way to work my temp reached the first touch of red I think it's like 255-260. So I park my car and pop the hood expecting to see antifreeze boiling out of the overflow tank. But no, it was sitting at the normal "hot" mark. I even felt up against the tank and there was no hot antifreeze even in it. So now I guess it's the temp sensor for the gauge. Does that sound like the solution to you all?

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91'Z28 305 TPI *stock for now*

 

I'd start with replacing the sensor, but before that look at the wire that goes to it and confirm that there's no insulation burned off from it which could make it short out on something metal.
If the sensor/wire doesn't fix it, there may be a problem in the printed circuit on the back of the gauge cluster.

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D.R. Stevens
1984 Trans Am 305HO L69
1991 Firebird 305 L03

 

Yeah those are some good ideas, thx. One thing that bothers me a little is that it wont jump around when its warming up. It doesn't happen until it starts getting hot at an idle.