Answer: You should have your differential fluid replaced according to your owner’s manual and manufacturer’s recommendation. Typically, your differential fluid should be replaced from 15,000 to 30,000 miles. Many vehicles are different, and you should consult your owner’s manual for the recommended mileage. When you have your fluid changed, you should also check all of the gears, shafts, and other parts in your differential for excessive wear in order to keep your differential working properly.