I had this problem a couple years ago too.I don't remember what I did. My heat had become eratic. I found the radiator to be very low on antifreeze so I refilled almost 1/2 gallon. The overflow did not need additional added. Isn't there a way to burped the system or something ??? Any other ideas ??
An air pocket in the cooling system could cause erratic heat. What engine does your Explorer have? Some cooling systems incorporate air purge valves, but often the thing to do is top off the radiator, start the engine and let it idle for a few minutes. Check the level in the radiator and continue to top it off. After several minutes if the level is no longer dropping, set the radiator cap to the pressure release/1st detent position and continue to let the engine heat up. Eventually the hot coolant will expand and find its way to the overflow/degas tank. Fill the degas tank to the full cold mark, put the radiator cap on fully, then shut the engine off and let it cool. As it cools it should pull coolant from the overflow tank to keep the radiator full, but you'll want to check the level in the radiator again once the engine is cool and top off if necessary.
Greetings and Happy New Year. My heating problem has returned. I never got full heat anyhow. I put in a new batch of anti freeze, themostat and new rad cap today. As I drained the AF at the drain ****. Black anti freeze came out of the radiator. On the upper cap side anti freeze was perfectly clean ????? Guess I need to have it flushed ???
A little history new used engine in 2010 87,000 actual miles runs fantastic. Replaced damn near everything. Blend door has been repaired there is a range warm to cold. The air cond. works perfect. I used to love to do this NOT anymore just trying to save some $$$$$$$$$$$$$$$$ MORE help appreciated. Here in Montana it gets cold.