I too have a 1999 expedition 5.4l with no heat/defrost. Had the tstat replaced today. No improvement.
Engine warms up into the middle of the temp gauge just fine. Engine runs fine and has never overheated. Coolant level is in normal range and not leaking.
Turning the heat on after the engine is warmed gives about 30 seconds of warm air, then the heater air cools down to just barely not cold. Turn the heat off, wait a couple minutes, turn it back on and the same thing happens.
Monday, November 26th, 2012 AT 10:35 PM