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Q: Radiator fans come on but very briefly. 5 seconds at the most. The car overheats when I get off the highway.

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Radiator fans come on briefly..5 seconds or less. Car overheats when i get off the highway. Sometimes when car overheats the heat turns cool then goes back to being hot. Had thermostat replaced and engine coolant temp sensor because car threw and code for that sensor. Still overheats from time to time

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

The first thing is to make sure the cooling system is indeed full. When the heat turns cold, this could be an electric problem or there could be an air bubble in the cooling system. A low cooling system can also affect the fan operation. The best method for checking the cooling system level is to remove the radiator cap first thing in the morning before you start the car. If coolant isn’t showing just under the radiator cap, top it off and make sure the coolant overflow container is filled to the appropriate mark.

If the cooling system is full, and the fan still turns off after five seconds, the cooling fan circuit will need to be diagnosed. With a symptom such as yours, it indicates there is a bad connection in one of the components of the cooling fan circuit. It is very common for electrical circuits to develop weak spots that fail shortly after they are turned on. Heat will build at the bad connection and stop electricity to flow. When the circuit is allowed to cool, it will again operate for a short time.

Possible component failures include the radiator fan, radiator fan relay, radiator fan switch, a bad connection at a connector and a fuse with a bad connection. The best spot to begin diagnosing the cooling fan is to pull the radiator fan relay and use a test light to check that the proper circuits are supplying power as well as use a jumper wire to supply power and or ground to the cooling fan to test the fan operation. Testing of this sort requires a wiring diagram, a test light and an understanding of electrical theory.

If you should require assistance with this, I would recommend having your car’s overheating issue inspected at your home by one of our mobile technicians.

Good luck!

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