Ive got a 99 v6 with about 130K miles on it. It's getting cold down here, and all the sudden my heat isn't working. As soon as the engine finally warms up, the heat will work for maybe two minutes max, then run cold again. I asked the local shop mustang buff about it, he said replace the thermostat. Did that. Still freaking cold. I know it could also possibly be the heater core, but I'm not smelling antifreeze in the car and the passenger side floor isn't wet. Any ideas?