I have a 78 Camaro and I noticed my temp gauge reads 260 degrees at operating temperature. I checked the temperature of the engine with my heat gun and it reads 190. I replaced the gauge thinking it was the problem and I then replaced the temperature sensor. It still reads 260. Is it grounding out somewhere or what?

Hi. When you start the engine cold, does the gauge evolve normaly and gradualy when heating up or does the gauge jump straight to 260°.