Learn What To Do If Your Car’s Thermostat Is Stuck

Attribution Some rights reserved by mah_japan

The thermostat in your car is responsible for controlling the amount of coolant released into your engine. When your car first starts up, the thermostat is closed and does not allow coolant into the engine until it is warmed up. The thermostat should open and allow coolant in once the engine is adequately heated. Sometimes the thermostat fails and remains closed. This article will discuss how to tell if your car’s thermostat is stuck closed.

Method 1

Testing at Home

  1. Check your temperature gauge in the car. A stuck thermostat might be to blame if your gauge marker nears the red danger zone within five to 15 minutes.
  2. Turn off your car and allow it to cool before opening the hood. Unhook your coolant reservoir if you can undo it and pour the antifreeze into a container. Locate your radiator and remove the cap.
  3. Unfasten the radiator drain cock located near the bottom of the radiator and allow some of the coolant to drain out into a container with a lid until the level is below the upper radiator hose.
    • You might not need to drain the radiator, depending on the amount your reservoir holds. The amount drained is roughly 1 to 2 qt. (4 to 8 cups). You can reuse this coolant if it is brand new. Otherwise, replace it with new coolant.
  4. Locate your thermostat. The thermostat housing is usually under the upper radiator hose. Unbolt the housing and remove the thermostat, using a screwdriver and pliers. Take the thermostat inside. There will generally be a number somewhere on the body, giving it’s opening temperature usually between 160 to 190°F or 70 to 90°C. Otherwise you will need to check the Workshop Manual for the car.
  5. Fill a pan with water and place the thermostat into the water until it’s completely submerged. Ensure that the part does not touch the bottom of the pan.
  6. Start heating the water and place a cooking thermometer into the water.Check the temperature frequently while monitoring the thermostat.
    • The thermostat should remain closed until it just about reaches the thermostat-opening temperature designated on the body (or in the Workshop Manual). At this temperature, you should see the thermostat begin to open.
    • The part should be completely open when the water reaches approximately 10 degrees above the reading on the thermostat. If the thermostat is still closed at this point, it needs to replaced.

Article provided by wikiHow, a wiki that is building the world’s largest and highest quality how-to manual. Please edit this article and find author credits at the original wikiHow article on How to Tell if Your Car’s Thermostat is Stuck Closed. Content on wikiHow can be shared under a Creative Commons License.

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