Mechanic suspects that Dex-Cool corroded head gasket and caused it to blow. Coolant was burning off and getting low, requiring it to be refilled weekly. This leak also introduced air into cooling system, causing heat to stop blowing hot and cooling to boil since the system was no longer pressurized correctly. When coolant boiled, it dumped out of the overflow tube and got even lower. Eventually it caused the engine to overheat due to low coolant and air in the system. Air can be bled out but the leaking head gasket would reintroduce it quickly.

This car has had issues with over heating for years. It started off with it over heating in the summer time while idling with AC on and has now recently turned into all the time. I just replaced thermostat and sensor but it still over heated when I drove away from the shop. It is now there waiting to be looked at again tomorrow for a possible blown head gasket but the mechanic said it is not showing any signs of that. It seems to be some how related to the heater being on? When the heater is on it over heats and stays hot but when the heater is off it will get hot but cools off while driving getting warm only when stopping. PTFO!!