Testing Your Thermostat

*VERY EASY*

You can test the operation of your thermostat without removing it from the engine by performing this procedure:

  1. Park the vehicle on level ground in a well-ventilated, outdoor area with the engine OFF, the parking brake engaged, and the transmission in PARK (for automatic) or REVERSE (for manual). If the engine has been run recently, let it cool. Raise the hood.
  2. Relieve any pressure at the radiator cap and remove the cap from the radiator filler neck. Start the engine and insert a thermometer (capable of reading 200° F.) into the coolant at the filler neck. Do not let the thermometer fall into the radiator.
  3. Observe the temperature and action of the coolant. If the coolant is motionless during the engine warm-up, then quickly rises in temperature and levels off, the thermostat is working properly. However, if the coolant begins to stir after the engine is started and its temperature rises immediately afterwards, leveling off somewhere between 120° F. and 150° F., the thermostat is stuck open (or even missing) and must be replaced.
  4. Replace the radiator cap and close the hood.

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