Hey, you could have a stopped up heater core, I've never changed one in an explorer, but I have in other ford b bodies and it's a snap. My 92 X has great heat after about 5 minutes, even on the single digit days, so it's not endemic to x's, bronco II's, and rangers, I've owned all 3 and they all had great heaters. If the fan spins easily when cold and engine off, the fan clutch is working properly when cold, heat the engine up to full operating temp, then shut it off, the fan should be noticeably stiffer to turn. It's also possible but much less likely that your heater hoses are collapsing, I'd probably replace the T stat with a known good 195 degree one (buy 3 cheap ones at autozone, etc boil them in a pot of water and keep the one that opens fullest, take the other 2 back), the radiator and heater hoses and the heater core. make sure to go thru several heat/cool cycles topping off the coolant several times till all the air is gone, you can use the resevoir for the topping off, no need to remove the radiator cap, just keep the resevoir topped off till it no longer needs coolant added to it. Good Luck.
