The temp gauge on my 1990 police caprice is out of whack. it reads a bizzare number every time I turn it on even though the car is not warm yet (i.e as soon as I turn it on it reads 220 ish then after 2-4 min it goes off the chart, the car doesn't overheat or anything like that). I have changed the Thermostat, the coolant temp sensor, and its still messed up. The batter gauge and oil pressure gauge work fine. Do you guys think it is a wiring Issue? if yes, does anyone have a ball park idea of how much it will cost to fix it.

PS my next step was to change the coolant temperature sensor switch.

 

It sounds like either your temp sensor for your gauge on the side of the exhaust manifold or the temp sensor for the ECM on the front of your exhaust manifold!