There's more than one mode of failure for a head gasket. It seals 3 different systems from each other. Combustion, coolant, and oil. Any could leak to the other depending on the failure. Each would produce different symptoms.
Originally Posted By: Noey
So many responses, so much misinformation...
A head gasket fails when there's oil in the coolant. What you're describing sounds more like coolant that needs to be changed, especially if you've just bought it and has an unknown service history. Coolant that has lost it's juice from time boils out and expands into the tank.
It's always good practice to change out all the fluids when you buy a used car..don't forget the brake fluid, too.