It does sound like a head gasket issue but other things should be ruled out first. Start with a cooling system pressure test to see if the source of the leak can be identified. Typically you will see white smoke from the tail pipe when coolant is leaking into the engine, but coolant can go into the oil too. If that's the case, the oil level will be too high. Get that fixed right away because a head gasket and oil change will take care of it. If you wait, antifreeze will melt the soft outer layer of the engine bearings resulting in more repairs to the engine.
When coolant leaks into the engine, it is also possible for combustion gases to get into the cooling system. Normally air pockets will work their way out of the cooling system but if more air keeps seeping in, those air pockets can cause coolant to stop flowing. Air in the heater core prevents coolant from circulating, and air by the thermostat prevents it from opening properly. Thermostats respond to hot liquid, not hot air.
Your mechanic can also perform a "sniffer" test at the radiator to check for a leaking head gasket. That involves drawing air from the radiator through a glass tube partially filled with a dark blue liquid. In the presence of combustion gases, that liquid will turn bright yellow. That is conclusive for a leaking head gasket, but there are other places the gasket can leak that don't show up in the cooling system.
Thursday, January 20th, 2011 AT 7:10 AM