1995 Pontiac grand prix's temp gauge goes hot

TEMPERATURE GAUGE IS MORE LIKELY BROKEN.

you may have a bad temp light sensor in the motor or gauge.170 is not hot at all for these cars.

THE COOLING FAN DOESNT COME ON TILL 220 CHECK IT WITH A SCANNER AND SEE WHAT THE TEMP THAT THE COMPUTER IS SEEING

maybe a water pump.

sensor might be dirty, try removing them and cleaning them. Dont use sprays as they pose a threat more than they fix. Check tires to see if there is one that might be WAY lower than the rest. Or consider taking it to a shop if you cant find the rigth abs sensor.

its either of the 3 ur water pump is weak and couldnt supply the right amount of coolant to ur engine / ur radiator is clogged or your thermostatic valve is stuck up that restrict full flow of fluid to the radiator thats why when u use the heater that uses ur coolant hot water as a heating unit the temp. goes down...

Did you bleed the radiator after refilling because it sure sounds like you have an air lock in there.

yes. but check every thing else first. coolant level being the most important. then the thermostat.

Replace the temp sensor/switch located on the radiator.  Don't forget to drain your radiator and use teflon tape on the sensor when installing it.  DO NOT over-tighten.

change the sending unit to the fan, if that doesnt work check for power too the fan or even a bad fan