no where to be found. If your coolant is disappearing, not showing up a a green leak of fluid on your garage floor, abd you car overheats, then you can suspect the head gasket. There is a chemical that will change color if combustion gases get in the coolant. I have never used it but will next time faced with this issue.
Many other things can cause overheating. head gasket is the one to overrule asap.