95 Grand Am 2.3 dohc 3spd auto -- thermostat

[Hutch750kz]

Hi, Sorry for the book here but wanted to give all info I could. I submitted this topic to 10w40 and read some of Ven's answers to other questions that impressed me so am asking for a Venturi opinion. 95 Grand Am has 202,000 miles on engine and trans and still runs very good. Five months ago ( a couple months after purchase) coolent temp elevated and loss of coolent. Refilled lost coolent and no more temperature problems until recently. Oh, Did notice slight antifreeze smell when first turning on heat (small leak in heater core?). Anyway, recently coolent temp again elevated and loss of coolent. This time refill did not correct symptom; I suspected sticking thermostat and purchased one.
Went to change thermostat and found it is located at water pump and decided to let trained mechanic change it. The shop explained later that they decided to test my system before the time consuming job of thermostat replacement. They found my head gasket blown/leaking and explained that the thermostat was ok and the overheating likely was from exhaust gases superheating the coolent. I thought
Does this sound reasonable? I believe I may have a head gasket leak but the temp gauge heats up quick like the thermostat is not opening. With the number of miles on this car I can't see getting the valve job/ head gasket replacement. I would like to get a few more miles out of it though but of course can't if it keeps overheating. If I can stop the overheating with a thermostat(any pointers here?), What damage or other problems may come from the head gasket leak? It does not show signs of being in the oil. thanks for any sugestions, Hutch

[Hutch750kz]

Update: I had a shop change the thermostat and it overheated before I got 100 yards away; let it cool and went back. They said there must be an air bubble in coolant line and they released the air -- I am not sure how as there is no cap on the radiator. It ran fine after that. Now at 212,000 miles runs strong. started over heating again intermittently then always after about a mile. I did put some stop leak in it in hopes it would seal any small leaks but it didn't seem to help. Quit driving for awhile except to start and drive around the block until warm every couple weeks or for short trips less than a mile. Now It won't overheat no matter how far I drive it - well I don't plan on taking this vehicle on any long trips - but it seems to be fine now! I am now suspecting the water pump is just going out and works intermittently. Any ideas?

By the way, the three speed auto trans is now only running on 1st and 3rd. Second started slipping; added Lucas trans stop-slip and it helped for awhile then it just quit going into 2nd stays in 1st longer and then goes into 3rd -- good thing the engine is strong enough to rev higher.

Also when it rains - water leaks in through the firewall into the passenger floorboard due to rust. Looks like this was previously fixed with some sort of aluminum sheet and some sticky black stuff but it is coming in next to that - I could put some more next to it if I knew what it is.
???