Toyota specifies 75W-85 GL-5 gear oil for the rear differential on every 4th and 5th gen 4Runner. Capacity is whatever the housing holds to the fill port — plan on roughly 3 quarts and buy 4. There is no drain interval published for normal driving; the practical answer is 30,000 miles, or 15,000 if you tow, carry roof weight, or wheel hard. It is a 30-45 minute job with one socket and a hand pump. And the single most important warning on this page: the transfer case takes a completely different oil. Do not fill it with what you put in the diffs.
What Toyota specifies: Toyota Genuine Differential Gear Oil LT 75W-85 GL-5, part number 08885-02506, in both the front and rear differentials.
What most people actually use: 75W-90 GL-5 full synthetic, because 75W-85 is scarce at parts counters and Toyota's own supply has been intermittent. This substitution is enormously common across the 4Runner, Tacoma, and Tundra platforms, and there is no documented pattern of differential failures attributed to it. If you tow near GVWR or live somewhere summer pavement bakes, the slightly heavier 75W-90 is arguably the better choice anyway.
What to actually buy: a full synthetic GL-5 in either weight from a reputable brand — Toyota, Valvoline SynPower, Mobil 1, Amsoil Severe Gear, Red Line, or Royal Purple. Skip the conventional gear oil. The price difference over a 30,000-mile interval is a few dollars.
Friction modifier: not needed. The factory rear differential on an SR5 or Limited is open, and the Auto LSD on those trims is a brake-based traction function that does not touch the differential at all. TRD Off-Road and TRD Pro models use an electric locker, which is a mechanical dog-clutch engagement, not a clutch-pack limited slip. None of these want a friction modifier. If you have installed an aftermarket clutch-type LSD, follow that manufacturer's instruction instead.
The transfer case trap, again. Toyota calls for SAE 75W LF transfer gear oil in the transfer case — a different, much lighter, much harder-to-find fluid. Red Line MT-LV 70W/75W GL-4 is the manufacturer-confirmed direct replacement. Filling the transfer case with 75W-90 GL-5 is one of the most common mistakes on this platform. See 4runner-transfer-case-fluid-4runner before you do all three at once.
The 4Runner rear axle is a Toyota drop-out third-member design — the ring and pinion assembly installs through the front of the housing, not behind a removable rear cover. That is why you will not find a cover to pull and a gasket to scrape. Drain and fill plugs only, which makes this one of the least messy differential services on any truck.
4th gen (2003-2009) trucks run the 8-inch rear. 2010 and later 5th gen trucks got an improved 8.2-inch rear with shimmed side adjusters, more ring gear bolts, and larger bearings — a meaningfully stronger axle and the reason 5th gen owners can run 33s and a locker without much anxiety. Both take the same fluid and the same service procedure.
Both plugs are 24mm hex heads on most years; a few use a 10mm internal hex. Both use single-use crush gaskets — 90430-24003 for the drain, 12157-10010 for the fill, about $2 each. Buy them. Reusing a crushed gasket is how a clean job turns into a slow weep that stains your driveway for the next two years.
Fill plug first. Every time. It is the one sequencing rule on this job and ignoring it can strand you.
Check the breather. The differential breather vents pressure as the housing heats. If the hose is cracked, pinched, or its cap is clogged, a hot axle dropped into cold water pulls water past the seals — and water in gear oil destroys bearings quickly. Many owners relocate the breather high into the body with a hose extension. If your 4Runner sees water above the hubs, drain the diff within a week of the crossing and look for milky contamination.
Read the magnet honestly. Metallic paste is fine. Flakes and chips are not, and a rear axle rebuild is a $2,000+ conversation. Finding it at a fluid change is exactly why fluid changes are worth doing.
Do not overtighten the plugs. They seal on the crush gasket, not on thread torque. Stripping a fill plug thread in an aluminum-free but still finite steel housing is an avoidable, expensive mistake.
75W-85 usually needs an online order. Toyota's own fluid goes on national backorder periodically. Order it a week ahead or plan on the 75W-90 substitution.
Set the interval to how you use the truck. Toyota's guidance is 15,000 miles under heavy load, roof-mounted gear, or sustained towing, and inspection-based intervals otherwise. Thirty thousand miles is the reasonable default for a weekend-wheeling truck. If you regularly ford water or run deep silt, tighten it.
| Item | Cost |
|---|---|
| Toyota 08885-02506 75W-85, 3-4 quarts | $54-72 |
| Aftermarket synthetic 75W-90, 3-4 quarts | $39-56 |
| Crush gaskets (drain + fill) | $4 |
| Fluid transfer hand pump (one-time) | $12-20 |
| Shop labor, rear diff service | $90-150 |
Doing all three driveline fluids at once — front diff, rear diff, transfer case — is the efficient move since the truck is already up and warm. Budget around $120-160 in fluid for the set if you use the Toyota transfer case oil, less with the Red Line substitute. Related: 4runner-front-diff-fluid-4runner.
| Part | Vendor | Est. price |
|---|---|---|
| Toyota Genuine Differential Gear Oil LT 75W-85 GL-5 (quart) | Toyota | ~$18 |
| Valvoline SynPower / Mobil 1 / Amsoil 75W-90 GL-5 full synthetic (accepted substitute) | Valvoline / Mobil 1 / Amsoil | ~$13 |
| Drain plug crush gasket | Toyota | ~$2 |
| Fill plug crush gasket | Toyota | ~$2 |
| Fluid transfer hand pump with flexible tube | generic | ~$15 |
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.
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