pull the spark plugs and see if one looks a lot different than the others!!=head gasket
Pull one plug from each cylinder and look for signs of coolant.
Bad head gasket symptoms
Quote
White smoke coming from the tailpipe. BUBBLING IN THE RADIATOR AND COOLANT RESERVOIR. unexplained coolant loss with no leaks. Milky white coloration in the oil. Engine overheating.
Just because it doesn't seem to run bad for now doesn't mean there isn't a head gasket problem.