91 Accord here and I'm trying to determine if I can tell by observing the coolant level fluctuation in the expansion tank to know if I have air in my engine cooling system? I suspect that if I have air in the cooling system that the expansion tank coolant level will remain static whether the engine is stone cold or has been driven for 30 minutes. Is this an accurate observation? I find it odd that my coolant expansion tank barely changes level (only about 1/4" at most) between cold engine and hot engine. I never paid attention to the coolant level fluctuation in the expansion tank before so I do not know if my 1/4" change is normal?

I think air contamination, I don't know how much it would take, in the engine cooling system would disrupt the flow of hot coolant into the expansion tank when the engine is hot and also disrupt the vacuum needed to remove coolant from the expansion tank when the engine cools back down once parked overnight. Thus, the expansion tank level would remain static/not change much at all times if there's too many air pockets in the cooling system??

Any thoughts anyone?

Dave.