I put my car up on the lift a week ago and yesterday when I came into the garage most of the coolant had leaked out and there wasn't enough left to see where it was coming from. When I cracked the coolant cap there was a big rush of our out of the expansion tank. I refilled it with water, ran it up to operating temp, about 200 degrees, let is sit for over 90 minutes, during which time there was no leaks, hissing, etc. I then opened the radiator cap and again had a big rush of air out of the system. Can anyone give me an idea of what might be going on?

Blown headgasket, cracked head, or cracked block.

Two ways to verify:

One, chemical tester that sniffs the air in the overflow tank for combustion gasses. The fluid color will change to indicate the failure or not.

Two, put at pressure gauge on the coolant overflow tank. Start the engine cold, rev up the engine, if the combustion is getting past the headgasket it will show right away as a pressure spike on the gauge.

Good luck.