im sure the car has a metal mls head gasket, they do not leak or blow like a standard gasket, they only lift when presure is too great then when the car is off the will seal back up and work normal, making many tests hard to do, is you coolant level low? i would use a simple coolant dye they sell at napa, a few drops in your overflow tank and the dye will tell you if theres any combustion residue in it, that is the easiest and simplest way to test the head gasket