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Q: Car Overheating

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I just topped off my coolant, but my car temp is still getting very high and close to over heating within two miles of starting to drive. There is no noise from the water pump. Is is possible that I just need to replace the thermostat?

A: If your coolant level was really low and yo...

If your coolant level was really low and you added coolant you could have air trapped in the system that creates a block to normal circulation. There are little weep holes set high in the coolant "piping" that allow you to purge air as you add coolant. Normally, these are opened when you are refilling a totally empty system in order to avoid trapping air and creating a blockage.

A malfunctioning thermostat is a common cause of overheating but before you condemn the thermostat make sure radiator electric fan(s) are fully functional, radiator is not obstructed with external debris, radiator is not internally plugged with sludge, and you don’t have a collapsed rubber coolant hose. There are some checks a mechanic can do to try to assess flow rate to see if thermostat is not open and/or radiator is plugged.

Note that if car is seriously overheating, you can easily cause significant damage to the engine via warping of the head and/or block. If it’s overheating at all, the prudent thing is to not drive the car until it is repaired; that will help you avoid needless additional problems. YourMechanic can evaluate the overheating situation for you and will be pleased to do so.

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