Originally Posted by smokeywren

Ford says your axle (differential) lube oil is good for 150,000 miles, unless the axle has been dunked in water. So if your diff has not been dunked in water above the vent tube, then no need to change the diff lube until at least 100,000 miles.


But if you suspect the diff has been dunked in water above the vent tube, you should change the diff lube immediately. Water in the diff lube will ruin the diff in a very few miles.