compression test = bad headgasket or rings?

[Jordan325iC]

What prompted the compression test in the first place was coolant boiling out of the reservoir after a 15 minute drive. Can't find any coolant leaks. Turbocharged engine, questionable tune, recently rebuilt engine (less than 500 miles).

Numbers for the engine, mildly warm (firewall to radiator):
135
75
125
150
150
150

Numbers for engine, mildly warm, with 1-2 tablespoons of oil:
150
125
155
150
150
150

Plugs all look good, none are fouled/carboned. Haven't noticed any smoke from the exhaust.

Now I know oil increasing the compression test numbers = bad rings. But I'm thinking maybe I put too much oil in the cylinders and the oil actually sealed a headgasket leak? But shouldn't headgasket leak mean two really low cylinders? Thoughts?

[Dissembler]

Yes, if compression increases byoiling the cylinders does generally indicate bad rings, but to be really sure get a leak down test done. With the piston at TDC a leak down test will tell you exactly whats leaking. Also note, that compression tests are only accurate if the engine is at operating temp, "mildly warm" may not be giving you accurate results.

A head gasket leak is more likely to manifest itself as oil in your coolant, or you'll see that if you open the coolant resevoir cap, it will bubble continuously. The larger the leak, the bigger/more bubbles will appear.