Q: Intermittent overheating

asked by on October 26, 2016

Car overheats after driving on the highway. Fans come on but very briefly. Maybe 5 or 10 seconds. No leaks. Had thermostat replaced and radiator cap.

My car has 158000 miles.
My car has a manual transmission.

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Hey there. This may suggest that the coolant fan relay switch may not be working properly. When you car is moving down the freeway at higher speeds, the engine gets a lot of cooling assistance just simply from the air passing through the radiator and into the engine bay which can cause an otherwise overheating situation to not be as noticeable until the car slows down or comes to a stop. When the coolant temperature reaches a certain point, there is a relay that triggers the coolant fans to come and then tells them when to turn off once the coolant has cooled down sufficiently. When this is not working properly you may notice the temperature moving up and down erratically like this. If you need further help having this resolved, a certified technician from YourMechanic can come to your car’s location to diagnose the overheating issue and guide you through any needed repairs.

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