Use Toyota WS ATF only. A drain-and-fill swaps about 4 quarts (40% of total), so do it three times spaced a few hundred miles apart to refresh the full system. Final fill level must be set at 95–115°F transmission temp — that part is non-negotiable.
Toyota calls the WS transmission "lifetime fill" and gives no service interval. The trucks that go 250,000 miles got serviced anyway, and the ones that don't go that far usually have an owner who believed the manual. Plan on a drain-and-fill every 60,000 miles to keep the fluid healthy, more often if you tow.
The big constraint: the 5-speed A750F (2005–2015) and the 6-speed AC60F (2016–2023) both have sealed pans with no dipstick. The fluid level is set by an overflow tube — you fill from below, run the truck through the gears at the right fluid temperature, and let the excess drip out the overflow. Get the temperature wrong and you will be 30% over or under, which kills the trans within months. You need an OBD2 scanner that reads ATF temp or a non-contact thermometer pointed at the pan. The target window is 95–115°F (35–46°C).
Total system capacity is about 10 quarts. A pan drain only releases about 4 quarts because the torque converter and cooler lines hold the rest. The accepted way to fully refresh the fluid without a flush machine is three drain-and-fills spaced 300–500 miles apart. Each round dilutes the old fluid, and after three you are at ~80% fresh fluid — comparable to a full machine flush at half the cost.
Use Toyota Genuine WS only, or a real WS-spec equivalent like Aisin AFW+ (Aisin actually builds the transmission for Toyota). Do not use Dexron VI, Mercon V, or universal "multi-vehicle" ATFs — the WS fluid is engineered for low viscosity and the wrong fluid causes shift slippage and overheating within 50 miles.
The fill plug is on the side of the trans housing, accessed with a 24mm socket. The drain plug is on the bottom of the pan, 14mm hex (Allen) bit. There is an inner overflow tube inside the fill plug threads — a 5mm hex (Allen) — that you only touch if you are setting the final level. Open the outer fill plug first to confirm you have a way to refill before you drain.
| Part | Vendor | Est. price |
|---|---|---|
| Toyota Genuine WS ATF (1 qt) — 5-speed needs 4 qt per drain, 6-speed needs ~4.2 qt | Toyota | ~$12 |
| Aisin AFW+ (alternative, 1 gal) | Aisin | ~$40 |
| Drain plug gasket / crush washer | Toyota | ~$2 |
| Fill plug gasket (overflow tube) | 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.