my 1999 grand prix, temperature gauge goes all the way to hot when the car is first turned
and stays there until the key is turned off
Sounds like the sending unit is bad. To test it, unplug the electrical connector from the sending unit. It's located right under the thermostat housing. Start the engine. If thegauge now reads "cold" replace the sending unit. If the gauge still reads "hot" wiring is shorted to ground or instrument cluster is bad. Note: when performing the above test your "service engine soon" light may come on. This is normal. The sending unit for the gauge is also the coolant temperature sensor for the computer. Once you plug it back in the light will go out. HTH. -Jim
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