How to Tell If Your Car Thermostat Gage Needs Repair

by Sabah Karimi

The car's thermostat gauge measures the internal temperature of the engine. The thermostat valve opens gradually when the engine reaches the 200-degree mark to allow coolant to circulate throughout the engine. If the thermostat gauge is not working properly, you will not be receiving an accurate reading of the car's internal temperature. Fortunately, there are several ways to tell if your car thermostat gauge needs to be repaired.

Step 1

Check your radiator cap. If the radiator cap is not securely in place, the thermostat reading can be inaccurate. Make sure the radiator cap is on securely by tightening it clockwise.

Step 2

Monitor the thermostat gauge for rapid fluctuations. If the gauge does not move when the car has been running for several minutes, or the gauge is in the "red" or danger zone shortly after starting the car, the gauge may be broken and is giving you an inaccurate reading. If the thermostat is fluctuating rapidly between 80 and 100 degrees while you drive, this is another sign that the gauge needs repair.

Step 3

Check the thermostat gauge reading when the car is idle. If the gauge is moving from normal to cold within a few seconds when the car is moving slowly or idling, the gauge could be broken.

Step 4

Check your temperature sensor. Locate the temperature sensor; it is typically located on the cylinder head near the hose flanges and has a green connector with two pins. Remove the sensor and place it in a cup of hot water with the key in the on position in the ignition and see if the thermostat registers the temperature of the water. If the gauge does not move, it may be in need of repair.