Q: Sporadically overheating

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My car overheats at the most random of times. Used to be very frequent but I changed the thermostat and burped the cooling system. Now it may be once every week/week and a half. I changed the thermostat twice, mechanics thought it may be faulty. They are now thinking it's the head gasket. We used a sealant and it drove fine for 2 weeks and the temp gauge started jumping up and down and then stayed up (the next morning was fine again). I really don't want to believe it's the head gasket. I looked up head gasket symptoms and they don't seem to fit, except the overheating. Oil and coolant levels are fine. I have a new water pump, radiator, thermostat, and fan. Also, what does a compression test do? I was told to do that to see if it is the head gasket. Thank you for your help in advance!

My car has 171000 miles.
My car has an automatic transmission.

Hi There, It sounds like you may possibly have a blown head gasket, but performing a compression test will certainly help to narrow this down. A compression test will indocate how much compression (PSI) is present in each cylinder. If any of the cylinders are lower than normal or if one of them is drastically out of line with the others, this may indicate you have a blown head gasket. A blown head gasket may cause a number of different symptoms. A head gasket that fails between cylinders will generally cause a misfire and potentially compression leaks from one cylinder into another. Low compression will eventually result in a rough idling engine. When the head gasket fails between a cylinder and the coolant port, coolant may leak into the cylinder causing it to be burnt with the fuel charge in the combustion chamber. This often results in misfires on startup, especially after the engine is run, turned off and restarted and in some cases may result in the engine not maintaining enough cylinder compression to even run or start. This type of failure may not always show with a compression test. I would recommend having an expert from YourMechanic come to your location to properly diagnose the symptoms you describe.

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