[thephantom1492]

My check list would be:
- coolant level in expension tank
- After driving for a bit, check the engine temperature. If the gauge say it's cold, and the engine temperature about match what the gauge say, I'ld assume that the gauge work fine
- Does the cooling fan turn on when cold? (beware of the A/C setting, which may be on at recirculation (max) and defroster, so might want to turn off the heat/blower. If it turn on, it might be the issue, investigate why it turn on when cold.
- Radiator hose, Are they matching the engine temperature?
- Thermostat might be faulty. They are normally designed to fail open.

Personally, I'ld suspect the thermostat. Else you have a multiple failure (temp gauge/sensor AND the heat selector thing (I'm unsure if it's a valve or a blend/mix door actuator (motor) that control the cold/heat on that car)

Water pump would cause engine overheating in no time, so the gauge would be quite high.