Toyota wants 75W-85 GL-5 in the rear diff of every 4th and 5th gen 4Runner; capacity is around 3.0 to 3.2 quarts, and the service is a 30-minute job once the rig is on jack stands.
The 4Runner rear differential is a wet-pinion housing under a stamped steel cover (no removable cover on most years, drain and fill plugs only). On 4th gen (2003–2009) the rear takes about 3.2 quarts and is open or factory locked depending on trim. On 5th gen (2010+) the rear diff on TRD Off-Road and TRD Pro models has a factory electric locker; on SR5 and Limited it's open or fitted with an Auto LSD that uses brake pressure to mimic limited slip — neither of these requires a friction additive.
The factory fluid spec is 75W-85 GL-5. Toyota sells it under part number 08885-02506. The challenge is finding it locally — most parts stores stock 75W-90 GL-5 instead. 75W-90 GL-5 is fully acceptable for a 4Runner that doesn't tow heavy. If you tow at GVWR or live where summer pavement bakes, the slightly thicker 75W-90 is arguably better. Stick with synthetic from a reputable brand: Valvoline, Mobil 1, Amsoil, Royal Purple, or Toyota.
The fill plug (24mm) sits on the rear face of the diff housing. The drain plug (24mm) sits at the bottom. Both use crush gaskets (parts 12157-10010 and 90430-24003) — replace them at every service, they're $2 each. Open the fill first to confirm it isn't seized. Drain. Reinstall drain at 36 ft-lbs. Pump fresh gear oil into the fill hole until it begins to overflow at the threshold of the port. Reinstall fill at 36 ft-lbs.
While you're there, check the rear breather hose for cracks or pinches — water crossings push water up the breather faster than past the seals. If your 4Runner sees water above the tire tops, plan to drain the diff within a week and look for milky contamination.
| Part | Vendor | Est. price |
|---|---|---|
| Toyota Genuine 75W-85 GL-5 Gear Oil (quart) | Toyota | ~$18 |
| Valvoline SynPower 75W-90 GL-5 (acceptable substitute) | AutoZone/RockAuto | ~$13 |
| Drain plug gasket | Toyota | ~$2 |
| Fill plug gasket | Toyota | ~$2 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.