An exhaust leak was found in my coolant while fixing an overheating problem. Im hoping it's not from a blown head gasket or a fine crack in the block. Engine runs like 85,000 miles should feel like and is normally aspirated. I was wondering if it is possible that exhaust gasses could have been sucked into my radiator reservoir and contaminated the coolant when I was topping off coolant with the engine running. I was in my garage with the tail pipes aimed outside but exhaust may have accumulated inside the garage. This may be just wishful thinking but hopefully it's a false positive. Any comments/opinions?

I have never heard of exhaust gases being mixed with coolant.

Are you saying it feels NA but isnt?
If you had a head gasket bad you'd most likely get antifreeze in your exhaust, the heat/steam will work its way into the combustion chamber. You'll have faint white smoke...or heavy. And it will smell sweet like antifreeze. Only thing you'd see in the radiator is some foamy bubbles maybe and maybe a tad of oil in it.

The engine has 85,000 miles on it and has never had forced induction or nitrous or any of that good stuff.

One of the tests you do when looking for an overheating problem is to check for CO (exhaust) in the cooling system. Many times when the defect in the head gasket is very small compression can push combustion chamber gases (very high pressure) into the cooling system (low pressure). Until the defect gets larger the 15 or so PSI in the cooling system cant push it’s way in to the cylinder yet.

Very good explanation. But is it possible that exhaust gasses collected in garage could have been sucked into coolant reservoir when I was topping off coolant level with engine running?

I'm kinda thinking that if exhaust fumes were heavy enough for that to happen, we might be reading an obit now, instead of a question.

Like I said, that was just wishful thinking. I guess the only way to be sure is to flush the coolant system out and retest at a later date. Also do a compression test. If both fail (worst case), ride it 'til it blows up, drop an LS7 and call it a day.

Most likely a blown head gasket. Start the car COLD with the coolant cap off. Let it warm up and check the coolant tank. If there is a exhaust leak, you will see bubbles in the tank. This would mean trapped gasses are making their way out.

I fa block test was performed using a liquid that changes color in the presense of CO2, then you do have a leak somewhere. Head gasket or crack in a cylinder head.

It sounds like the only way to effectively fix it is to tear the heads off to inspect the gaskets and/or have a pressure test done on the heads.

I would like to see a compression and leak down test done... That will tell the story. And believe me, its not always the story you want to hear

It turned out to be a bad coolant reservoir cap. It wasn't holding the pressure. That sure beats a blown head gasket or cracked head. My local dealership wanted to rip the heads off and inspect heads and block if I gave them $2700. The only reason why my car was at the dealership was because I thought this problem was associated with what they had previously worked on when it was still under warranty. They claimed it was leaking exhaust fumes in coolant. What did I do about it? I pulled my car and retested for exhaust leak. No exhaust leak was found! Geee Let me weigh this out. $10 cap or $2700 inspection I'll let you guys draw your own conclusion.

Oh and they did give me back my money that I paid them for labor and inspection so I wont name any names. Hopefully this situation wont happen to anyone else but I find that hard to believe.