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Q: Could it be the coolant sensor?

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My car keeps over heating. I replaced everything. Finally figured out that what ever tells my electric thermostat to open is not doing it's job. My heat had does not show that my car is running hot but it is. So we took the thermostat out and the car does not run hot is this my coolant sensor?

My car has 136000 miles.
My car has an automatic transmission.

A: Hi and thank you for contacting YourMechani...

Hi and thank you for contacting YourMechanic. If your vehicle engine is overheating, there are 3 different things that can cause this problem.

The first is the thermostat is not opening up. A stuck thermostat will cause an engine to overheat.

The second thing is a radiator or reservoir cap that will not hold pressure will cause the coolant to boil and make the engine overheat.

The third thing that could cause an engine to overheat is a burned head gasket making hot exhaust gasses into the cooling system and not properly conducting a heat exchange.

I recommend replacing the thermostat and the sensor. This eliminates the thermostat and signal for the thermostat. If the engine is still overheating, then replace the radiator or reservoir cap. If the engine still overheats, then it is possible that the engine has a burned head gasket.

You could get a block heater and place it over the radiator cap with the cap off and the engine running. When steam comes up, squeeze the plunger and allow the air to come in contact with the blue fluid inside the block tester. If the blue fluid changes color to orange or yellow, then the head gasket is burned. If the fluid does not change color, then it is possible that the water pump has failed.

To avoid any unnecessary repairs, I recommend having a certified professional, such as one from YourMechanic, diagnose the cooling system of your engine.

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