Also let me add, I had been driving about a 100 miles on the freeway, running between 65-75mph with a little jaunt to 100. When I got off the freeway I heard the knocking sound that I thought was the exhaust leak that had gotten worse (loose header to down pipe connector as I found in disassemble). About a mile later I got the temp light and shut it off immediately.
When I popped the hood, I found the coolant overflow was full and bubbling. With a rag, I carefully loosened the radiator cap and had steam coming out. Let it cool of and put a gallon of water in to get me the 1 mile home.
I ran compression test and all were between 145-160psi. Leakdown test showed no leaking of any cylinders. Ran a block test and no exhaust gases were found in the cooling system. I never lost power and outside of the noise, it was running well, outside of the mid range throttle ping/detonation.
