Well it's a longshot, but what the heck, live life dangerously. Park your Explorer on a steep hill with the front end facing uphill. Let it run for 15 minutes or longer to let the engine warm up to normal temp. During this time, have your heater control all the way over toward heat and let it stay there with the fan on low. Before you shut the engine off, make sure it has fully warmed up. Shut the engine off and make sure your radiator reservoir has plenty of coolant in it (full hot mark or above). Let it sit there overnight and cool. The next morning, check your reservoir to make sure it still has plenty (cold mark or better). Start the engine, drive it around and see if it has taken care of the problem. By doing this, you are giving the air that is in the heater core a chance to rise and be replaced by coolant. As the air rises, it will eventually circulate it to the radiator where it should stay and will eventually purge itself out thru the overflow into the reservoir when the engine is shut down.
As you probably know, as the engine warms up from cold, the coolant expands and is pushed into the reservoir. During the night, as the engine cools, it will actually pull coolant back into the radiator from the reservoir and the air should be gone. Just to be sure, take the radiator cap off in the morning and check the coolant level. If it is low, add coolant to the top of the neck.
You may have to do this a second night to be sure you have all of it. If this doesn't take care of the problem, you probably have a bad heater core or another problem.
Your heat fluctuations could be caused by air or a faulty thermostat. Try the procedure above first and after a couple of nights, if that doesn't take care of it, replace the thermostat.
Keep up posted. Dead Link Removed
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Ira
91 XLT 4x4
