Any liquid-cooled car engine has a small device called the thermostat that is located between the engine and the radiator. The thermostat in most cars is about 2 inches in diameter. Its task is to block the flow of coolant to the radiator until such time that the engine has warmed up. Considering the critical task that the thermostat does in the cooling system, it is important that you maintain it in good working condition. Here are the steps on how to check the thermostat:

Check the Thermostat While the Engine is Running

  • Locate the engine’s thermostat. It is normally found at the front of the engine.
  • Open the radiator cap and make certain that the radiator is full. Replace the radiator cap and start the engine.
  • Turn the vehicle’s heater on high then allow the engine to warm up for a few minutes. Be careful not to let the engine overheat.
  • Feel each of the hoses leading to and from the thermostat housing. If both hoses are hot and the heater is pushing out hot air. This is a clear indication that the thermostat is functioning properly.
  • If one of the hoses is cold, the thermostat may be stuck. You’ll need to remove the thermostat from the engine. Here are the steps to do so:
    1. Turn off the engine and allow the engine to cool.
    2. Remove the bolts holding the thermostat cap in place.
    3. Lift off the housing cap to expose the thermostat. Then pull the thermostat out of the housing.
    4. Put the thermostat in a pan of water on the stove and turn the burner on high.
    5. Monitor the water temperature with an oven thermometer. The thermostat should open at about 195 degrees F if it is functioning properly.
    6. Replace a faulty thermostat.
    7. Reinstall it if it opens and closes properly. Look for another problem in the cooling system.