It seems to heat fine for about the first 10 minutes, then the gauge starts to drop and it gets cold. In the fall I replaced the tbelt and t-stat, and last month I replaced the mfts. I had noticed a problem defrosting last week but with this sudden cold snap I realized the heat problem. I coiuld use some advise please.

Have you checked the coolant plumbing to tell whether what you're seeing is a gauge issue? I mean, have you tested the temperature of the hoses. If they're too hot to handle for any length of time after the gauge starts to read cooler, you have a gauge/sensor wiring or sensor problem. If the hoses go from hot to cool and stay there, your thermostat is sticking open like qpower says.

There's a motor that opens and closes the flap to allow fresh/cold air to blend in with the heated, recirculated air. When it dies, it tends to stick open and let in too much cold air.

Have you tried using the HVAC head diagnostics?

Thanks, no I havent tried the HVAC, guess I need to do so emore research. I think yopu may be right, the temp gauge doesnt drop until hwy speed, so I think it is just dropping because of the cold air, not the t-stat failure. And yesterday I ran the temp control from hot to cold and back again and heard a flap drop in the dash, suddenly it was blasting heat!