^^^idr how many miles are on this Explorer but I do remember why I had to drop the oil pan. It was clear that this car was very poorly maintained.
The dipstick showed that there was way too much oil in the engine and it looked very old. So, time for an oil change, right? Well, when I unbolted the drain plug nothing came out. Nothing! So we had to drop the pan and see what was up. Found an 1-2" layer of sludge in the pan. We scraped that clean and when we got the engine running ran cleaning solvent in the oil then did another oil change.
We also had to flush all the coolant. Pretty sure the reason the heater core went bad was someone mixed dexcool, the factory anti freeze, with green anti freeze. Never do that. Mix those coolants and they coagulate.