Heater core partially plugged | Ford Explorer Forums - Serious Explorations

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Heater core partially plugged


Explorer Addict
October 22, 2006
Reaction score
City, State
Huntington Beach, CA
Year, Model & Trim Level
98 XLT, OHV, 4D, 4x4, 5M
I recently reacquired my 1998 Explorer XLT that I gave to my brother about six years ago. He took it with him from NC to CA and drove it about 4 years. Two years ago, it got parked in front of his house and had been sitting there since until I recently also moved to CA and picked it up.

I just changed the water pump to fix a coolant leak and replaced all of the heater hoses, and heater valve. I ran some water through the core and got a bit of junk out. I noticed though that there's still not as much heat coming out of the vents as I would expect (I remember the heater on this thing to be scorching hot). The last thing I want to do is change out the core.

Anything I can add to my coolant to help free up deposits and/or preserve the core so it doesn't corrode? Should I just keep back flushing it with a garden hose?

Make sure the heater control valve (thing in engine compartmant with vacuum hose going to it) is opening all the way. I turn mine to heat every now and then just to kkeep the coolant moving through it. If you use the a/c all the time like I do (live in Fl) the waater rarely ever flows through it becase the controls are always set to cold, this could make the heater control valve stick due to lack of use and rust.

Thanks for the input, I actually replaced the heater control valve out of precaution even though I think the original was OK. (This valve actually only closes on MAX A/C anyway, but I had one rupture before so I figured it was cheap insurance)

I believe I found the culprit - a collapsed overflow bottle hose. I had tested it by blowing air through it, which it passed -- but I was suspicious when I would hear air hissing when opening the radiator cap after a drive indicating vacuum inside the cooling system. I think it was too soft and pinching shut under vacuum, and causing the system to be chronically underfilled and limiting the amount of fluid flowing through the heater core.

So far so good after replacing this hose with some general-purpose oil cooler hose.