I have had very low or no heater/defroster hot air output on my 97 Taurus GL
wagon (3.0 liter Vulcan with AC) since I used some Prestone Stop Leak to
(successfully) control a slow loss of coolant level. I suspect the coolant
loss was a due to very small head gasket leak, as there was no evidence of
external leakage at the ususal suspect locations, and no smell of leaking
coolant anywhere inside or outside of the car.
Back to the heater, since the Stop Leak was introduced, heat output has been
very low or non existent, though very infrequently, I do get some hot air
out. The engine and the rest of the cooling system is coming to normal
temperature, however, the return line on the heater is cool, indiciating to
me that the core is likely clogged, probably from the Stop Leak. The heater
bypass hose is hot, so it looks like everything else is OK.
I am going to try to backflush the heater core through its supply and return
hoses. Is this likely to clear the clogging? Assuming that it does not,
how difficult is it to actually change out the core? I've done this on a
few other cars, and it usually requires a massive dashboard disassembly.
Never done this on a car with dual air bags.
Am I overlooking something obvious, such as a stuck thermostat? I'm
thinking that's OK, based on otherwise normal coolant temperature gauge
readings, and the fact that flow in the bypass line, which appears to be
directly in parallel with the heater core, is hot.