My 1986 IROC temp gauge is completely at its high limit pegged), with the ignition turned off. It got stuck and I had to pull the face to free it. Otherwise it appears to work properly. Is it supposed to peg fully when it is cranking?

 

It will peg if you short the sensor wire directly to ground. If you unhook it, it should go to zero.

 

Fixed it! Since it was pegging, during cranking of engine, and getting stuck between the gauge face edge and metal faceplate, I decided to do some bending.

I took the temp gauge out; and slightly bent forward the housing tabs and their respective face mounts. The 2 are attached together with little rivets.

What this did was actually caused the temp gauge needle to move closer to the face of the gauge. I manually moved the needle full scale to check its limit. Now it stopped when it made contact with the raised outer edge of the temp gauge; and it did not rise up over the edge and get stuck, as was the original problem.

I reinstalled the temp gauge and face plate/glass, and tested it. when I turned it to "ON" it read cold (in this test, the engine was actually cold). When I turned the ign key to "START" the engine cranked and the gauge went to its highest full scale physical limit. When I moved the key from "START" back to "ON" the needle moved to is current temp reading (cold), and was no longer pegging and sticking. I tested it, after warming the engine, and the needle went to the normal operating temp after cranking. It's working great now.