I have a 2000 alero 3.4 w/ 144000 miles and it was missing off of a cold start for a while. And I had to add antifreeze once. I replaced the surge tank cap and I didn't have to add anymore. But I still had the missing. I bought a code scanner and it said it was missing on the #1 cylinder. I checked the spark plug and found that inside the ceramic it was rusty. ( I happened to have snapped it in half taking it out. It seemed to have broken easily. Maybe it was cracked already.) The end that sits in the head looked fine. No corrosion or anything. Just normal wear. Since I replaced the plug it has not recorded a missfire. But 2 days ago i drove it and it overheated. I replaced the thermostat and it now runs fine. I have not seen any white foamy oil or oil in my antifreeze. And it does not put out strange smoke from the tailpipe. Early on in this ordeal you might smell antifreeze when you were near my car but I never saw any anywhere, and not more than once or twice. It didn't throw any other codes. It has only overheated the one time. Should I buy a combustion leak detector and see what it says? And if so will it tell me if the manifold gasket is leaking or just the head?
Thanks in advance for your thoughts and suggestions.