[belldave]

I have an intermittent heat problem (inside the car) which I fear is masking a greater problem. The temp gauge, and thus heat inside the car, run normally in the city but drops to near minimum (thus cold air inside the car) after around 10 mins on the interstate. There appears to be air entering the cooling system which is causing this: I have twice "burped” the system, following which the engine and cooling system run normally (radiator hot, radiator fan blowing hot, no bubbling in water reservoirs, all cooling system pipes hot) until I’ve been at higher speeds for 10 mins or so, when it drops again – presumably due to more air being sucked into the system. The coolant levels do not appear to be dropping, nor is there any sign of coolant leakage from any area. Is it possible/likely that these symptoms point towards a head gasket or cylinder head problem? If so, have you any idea of repair costs for these faults (I guess the labor charges will be the greatest) – or even whether it is worth repairing? Many thanks in advance.