Replacing the differential fluid, also referred to as gear oil, in your Ford Expedition, is part of basic maintenance that should be performed periodically as outlined in the owner's manual. Gear oil breaks down just like engine oil does and loses its ability to properly lubricate the gears in the differential. Changing the gear oil in your differential is relatively easy and only requires basic tools.
Place a drain pan beneath the differential.
Place the square end of the 1/2"-ratchet in the drain plug located at the bottom of the differential and loosen it. Allow the gear oil to drain into the drain pan.
Put the drain plug back in the differential and tighten with the ratchet.
Remove the fill plug at the top of the differential in the same way that you removed the drain plug.
Fill the differential with gear oil until oil starts leaking out of the fill hole. Let the gear oil seep out until it no longer drains. It is very important to be patient and wait till it is done draining or else you will have differential problems.
Tighten the fill plug with a ratchet.
