Unfortunately, I think I Already know the answer, but I wanted to take to the forum to get an official consensus. Approximately 4000 miles ago I had my vehicle taken to the shop for an over heat Situation. I specifically asked the mechanic to make sure that the engine was in good working shape before any repairs were done. He assured me that it was. He then proceeded to replace quite a bit. When I say quite a bit, I mean the following; water pump, fan, thermostat, thermostat housing, radiator. Fast forward till today, I realize that my air conditioner is not blowing cold. I want to check my coolant, and although it does not seem low, I realize in this process that My coolant was bubbling. After some research the consensus seems to be that is a symptom of a head gasket issue. Is that a definitive answer? Are there any other potential causes of coolant bubbling In the reservoir? For what it’s worth, the engine sounds fine and I’m not overheating.

I have 212k on her. Thank you for your help.