HELP!!!!!!!!!!!! '92 Jetta heating system problems

temperature stays in the middle when you are driving?

bad heater box flaps allowing too much fresh air in? or a slight blockage in the heater hoses or core not allowing the coolant to flow freely. maybe you need to take off heater hoses at the engine and shoot some water from the garden hose through one hose and the the other flushing out the core.

was any coolant leak-stop used?

Thank you for your reply.

No Coolant leak stopper was ever used and the coolant was replaced with new phosphate free coolant every two years since I bought the vehicle new form the dealer.

The temp reads normal (in the middle, straight up). The heater works well when stationary and when you drive off onto the freeway the heat turns into cold air. This problem was never exerienced before.

The thermostat was replaced with an original VW with hopes of curing the problem.

Once I return to city trafic the heat will return.

This is all the info I have gathered.

The heater core seems to be buried deep into the dash. How can I diagnose the problem or "flush / clean" the heater core? I like the garden hose solution.

Check your vacuum hose through the firewall that controls the flaps. The hose might have come loose.

If the car has vacuum operated HVAC controls, this sounds like a pinhole leak in one of the hoses; the flaps will set correctly when the engine vacuum is high but will return to their "default" state when vacuum drops. Also if there's a check valve in there somewhere that might be suspect too.

good luck

nate