How to Tell if Your Car’s Thermostat Is Stuck Closed(will cause overheating)


The thermostat in your car is responsible for controlling the amount of coolant released into your engine. When your car first heats up, the thermostat closes 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.

How to test a thermostat DIY

Step 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 5 to 15 minutes.

Step 2. Allow engine to cool(never open the preasure cap of a radiator when its hot)

Step 3. Unfasten the radiator drain rooster 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.

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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.

Step 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.

Step 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.

Step 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 about 190 ºF (88 ºC). At this temperature, you should see the thermostat begin to open.
The part should be completely open when the water reaches 195 ºF (90.6 ºC). If the thermostat is still closed at this point, it needs to replaced.

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