If you continue to get air in the system, suspect a cylinder head gasket is leaking. When air sneaks into the cooling system, it can pool under the thermostat and prevent it from opening. Thermostats must be hit with hot liquid to open. Hot air will not do it. The air is what causes the thermostat to remain closed and the engine to overheat as a result.
Your mechanic can perform a chemical test to check for a leaking head gasket, but it is a little more difficult on GM cars because the engineers did not bother to put a cap on the radiator. The test involves drawing air, in this case, from the reservoir, while the engine is running, through a glass cylinder with two chambers partially-filled with a special dark blue liquid. If combustion gases are present, the liquid will turn bright yellow.
You can borrow this tester from an auto parts store that rents or borrows tools, but they will make you buy your own bottle of fluid. That is because it will be rendered ineffective if it freezes or becomes contaminated with coolant. They do not want to risk lending it to the next person with contaminated fluid, so everyone must buy their own. For that reason, it can be less expensive to just pay your mechanic to do this test. It just takes a few minutes.
Feb 27, 2018 at 10:57 AM
