Here's what you should check:
* Temperature Gauge: The gauge itself could be faulty. Try tapping it gently (carefully!) to see if the needle moves. A completely dead gauge suggests a problem with the gauge or its wiring. A fluctuating gauge also points to a problem.
* Temperature Sensor: The engine temperature sensor is what tells the gauge the engine's temperature. A faulty sensor will provide inaccurate readings or no reading at all. This is the most likely culprit. The sensor is usually located in the engine block or cylinder head. You'll need to consult your vehicle's repair manual to find its exact location.
* Wiring: Check the wiring between the temperature sensor and the gauge for any breaks, loose connections, or corrosion.
* Coolant Level: While unlikely if the heater is working, ensure your coolant level is sufficient. Low coolant could cause inconsistent readings, though typically the heater would be less effective in this case.
What you should NOT do: Ignore it. A faulty temperature gauge can lead to serious engine problems if you overheat your engine without realizing it. While your heater is currently working, this may change if the issue is ignored.
What you SHOULD do: Have a mechanic diagnose the problem as soon as possible. They can test the gauge, sensor, and wiring to pinpoint the fault and make the necessary repair. Driving with a malfunctioning temperature gauge is risky.
