How often should differential fluid be changed?

When should I change the rear differential fluid for my 2000 Ford F150 2WD with an axle code H9 (3.55 Limited Slip)? It has nearly 100,000 miles on it. The owner’s manual and Ford’s online maintenance schedule don’t specify an interval, only that you should use SAE 75W-140 fluid.

Although a 30k interval is advised, you can certainly get by with a 50–60 interval. Girlfriend drove her Jeep for ninety thousand miles, and it was well overdue.

Manual might not say, but here’s the deal on your F150 differential fluid:

  • Severe Use (towing, off-roading): Change around 30,000 miles.
  • Normal Use (everyday driving): Recommended change around 50,000-60,000 miles.

Your truck has 100,000 miles, so it’s likely due! Fresh fluid protects gears and bearings, especially important for your Limited Slip Differential (H9 code).

  • A mechanic can confirm the best interval for your situation.
  • Look for unusual noises or turning problems as signs of worn-out fluid.
  • Always use SAE 75W-140 fluid as recommended.

If you travel in water deep enough to submerge any of the gear boxes, change it every thirty kilometers or whenever possible. You will have a milkshake-like situation and unhappy bearings if water gets inside one of the transfer cases or differentials.