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Q: Temp gauge goes up and down

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The temp gauge goes up to ninety then goes back down

My car has 176000 miles.
My car has a manual transmission.

Hi There, This can be caused by a number of things such as a faulty thermostat, a clogged radiator or potentially a faulty cooling fan relay. The thermostat regulates the flow of the coolant in your car’s engine and controls when the coolant flows in and out of the motor from the radiator by opening and closing at specific temperatures. When your thermostat is not working properly or is stuck closed, this will not allow the coolant to properly circulate through the engine, which may cause the engine temperature to fluctuate erratically or in some cases just remain hot. When the thermostat is stuck open it can cause the coolant to circulate constantly resulting in the motor never reaching the correct operating temperature.

The typical electric cooling fan circuit includes a temperature sensor, a relay, a control module and the fan motor. The relay is the component that fails most often, so be sure to test the relay as well as its power supply and ground connections. A good relay coil will typically read 40 to 80 ohms. If resistance is high, the coil may still be working but it is failing, or it may not work when electrical loads are high. If the coil has no resistance, it is open and has failed and you will need to replace the relay. I would recommend having a professional from YourMechanic come to your location to diagnose and inspect your cooling system.

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