Make sure it's not something as simple as a coolant leak or a bad thermostat first. Buy a radiator flush kit, hook it up to a hose and look for leaks. Compression tests aren't always reliable indicators of a blown headgasket, though it seems like there's something funky going on with your compression if it gets lower when the engine is warmed up. I learned this the hard way this week assuming my friend's car had a blown headgasket when pressurizing the cooling system revealed myriad leaks spraying bleeding massive amounts of coolant under pressure. The guys on NABR were quick to point out my error in picking the worst case problem and running with the theory before doing any diagnosis and checking the easy stuff.

I wish I could come help you, but I'm leaving town for two days in about six hours. Sorry.