Join Date: Apr 2007
Location: Orpington, Kent
It is possible for a head gasket to leak for a long time, thousands of miles, before it fails totally. Hot gases then pressurise the cooling system and cause overheating. When the engine's cold, if you remove the radiator cap is there a hiss as pressure is released, and does the water level go down? If it does, then it sounds like the gasket. Hope it's not...
Other suspects (if those aren't the symptoms) would be the thermostat and the pump.