Throughout this thing, we kept hearing people say, "Bet your head gasket is bad." Well, we had no oil in the coolant and no coolant in the oil-we weren't losing any of either. Apparently, you can have a problem and not have leakage or loss. Often, it will show itself in the form of combustion gas in the coolant. This Block Tester from NAPA (PN 7001006) effectively sniffs the coolant to see if you have internal head or head gasket problems.