Time: aprrox 30 min

Difficulty: easy

Cost: $40-150 (oil preference, gasket replacement)

WHY

High temperatures and heavy loads break down the protective properties of gear oil over time. Gear wear and moisture from venting to atmosphere further contaminate the fluid which can lead to leaks and premature part failure.

WHEN

Replacing the rear differential fluid every 30-60,000 miles is good maintenance. Frequent start/stop driving, towing, high temperatures, or exposure to heavy dust or water might merit the earlier end of the range, while straight-and-level commuting would allow for a stretched-out interval.

METHOD

While some rear differentials have a drain plug, most do not. Most often, the rear cover is removed to drain the fluid and inspect the gears. The cover is then resealed, installed, and fluid added through the fill hole.

An alternate method is to use a fluid extractor. While this is quicker and easier, you may not get out all the settled grime.

If the fluid capacity is not known, general practice is to fill the differential with the recommended gear oil to just below the fill hole (approx 1/2"). This allows for fluid expansion when hot without overpressuring the seals or causing the oil to foam and cavitate.

The video below shows the fluid extraction method on a 2016 Ford F150.