I just purchased a 2006 chevy equinox awd v6 and I test drove it prior to purchase, left on idle with ac on while I scanned it with no warning signs of a head gasket leak or overheating. Driving 45 mins up a mountain, it began to overheat like there was air in the system, burped the coolant and bled it and was on my way in 10 min.
It seems air is entering the system somehow but there are no compression gasses coming from the coolant reservoir, no smoke from exhaust, and no boil over. I think the steps to follow are flush the system and replace thermostat after using a head gasket sealer just in case. Anything that would come to mind that would cause this issue occasionally
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I test drove it prior to purchase
But did you have a good mechanic check it out prior to purchase? Those are not exactly the most reliable vehicles around and that one is 19 years old. Note that head gasket problems are pretty common:
https://www.carcomplaints.com/Chevrolet/Equinox/2006/
Overheating can be a symptom of as well as the cause of a head gasket leak and head gaskets can leak in various ways that do not always result in combustion gases in the cooling system. If the gasket was not blown before it may be now due to the overheating incident.
I think the steps to follow are flush the system and replace thermostat after using a head gasket sealer just in case.
Why would you use a snake-oil product like a head gasket "sealer"? That kind of thing is a last desperate attempt to get a few more miles out of a beater when the only alternative is the junkyard. Not only is such a product a temporary band-aid at best, it may not work at all and can plug up your cooling system, making matters worse. One of our members found this out the hard way last year:
What you need to do is more troubleshooting to determine what is going on, though a cooling system flush and thermostat replacement is not a bad idea. If you are losing coolant use UV dye and/or a pressure test to find the leak.
