Many folks do not even know what the differential does. It is not one of those common car parts like the transmission or radiator. In fact, some people go the entire lifetime of a vehicle without knowing what the differential does.
What does the differential do?
Remember watching people run track during the Olympics? For longer races, after everyone starts out in his or her appropriate lanes, everyone clusters toward the inside lane of the track. That’s because, around curves, the inside lane is the only one that’s actually 400 meters. If the runners were required to run in their lane for a 400-meter race, the runner in the outside lane would actually have to run 408 meters.
As a vehicle goes around corners, that same scientific principle applies. As the car goes around a corner, the wheel on the outside of the turn is covering more ground than the wheel on the inside of the turn. While the difference is tiny, a car is a precision vehicle, and small variances can do a great deal of damage over the long run. The differential compensates for this difference. The differential fluid is a thick, dense fluid designed to keep the differential lubricated as it compensates for all of the turns that the vehicle makes.
How often do I need to replace the differential fluid?
Most manufacturers recommend that the differential fluid be changed every 30,000 to 60,000 miles. It is a messy job, and should be done by a licensed mechanic. The fluid will have to be disposed of properly, you may need a new gasket, and the parts inside the differential housing will need to be wiped down so that any contaminants from the old fluid aren’t transferred to the new. Plus, because the differential is underneath the car, it will need to be lifted, so this is definitely not a DIY project.