Compression can tell you if the head gasket is bad between cylinders but a leak down test will tell you for sure. Also there's a sniffer test to see if exhaust gases are in the coolant. You could have a craked head or block too. Did you overheat the motor recently? Are you using or loosing any coolant? Sometimes the condensation can form in the motor and not be burned off, especially if you moved the car to changed the oil.