Differentials, found on all vehicles FWD, RWD and 4WD in order to: Provide the drive wheels with the power being transferred from the engine. Reduce down the ratio of rotation for the last time “Gear Down”. Provide power to the wheels but still allowing them to rotate at independent speeds, allowing the vehicle to turn without issue.
A common misconception is that FWD vehicles don’t have differentials, this is incorrect, but these are most commonly lubricated from the gearbox oil and are very rarely separate.
Diff oil, car differential oil and axle oils do not need regular oil changes like engine fluids, this is generally because of them being isolated from the combustion process and the fact that they are in sealed compartments in the drive train, meaning they are protecting them from outside contaminations. However your car manufacturer will recommend a drain and replace timescale and over time some will need topping up. It is important that when topping up or replacing your diff oil / differential oil / axle oil that you use to correct oil specifications for your vehicle, always refer to your handbook for correct spec and viscosity.