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Q: My car runs hot and overheats

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My car was overheating so I booked an inspection through Your Mechanic a couple months ago. The radiator had a leak and the coolant was low. Other than that the mechaninc said everything else was ok. I had the radiator replaced and my car was running fine. Now it started running hot again and overheating. The coolant level seems ok and the fans work. I noticed on longer trips (es. 30 min on highway) the temp gauge sits half way until I arrive at destination and it spikes up. The temp gauge started reaching the halfway mark pretty soon, it wasn't like that after I had the radiator replaced.
What could it be? Thanks

A specialist from YourMechanic will surely be able to resolve this new issue for you. Of course, it is possible that the temperature gauge and/or the sending unit are malfunctioning and so that is the first to check. If, though, actual temperature measurements show that the engine is operating on the high side, in terms of temperature, one of the first things to suspect is the thermostat in the cooling system. If the thermostat is sticking slightly closed, that would create the symptom you are seeing. Another potential problem area is the water pump. The drive belt has to be tight so that the pump is driven at adequate RPM. Sometimes, a faulty radiator cap will contribute to overheating (the cap maintains pressure in the system, raising the boiling point of the coolant).

It is also possible that there is nothing wrong with the cooling system but instead the engine is operating on the lean side, in other words there is an engine or fuel system fault causing the car to run hotter than it should be. The simplest case would be something like a faulty thermostat but all of the possibilities I have noted have to be looked at in an engine overheating diagnostic.

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