Flush your 4Runner's brake fluid every 30,000 miles or 3 years; you need about 1 quart of DOT 3, a 10mm wrench, and clear tubing to do it right.
Brake fluid is hygroscopic — it absorbs moisture from the air. After three years, even sealed brake systems pick up enough water to drop the boiling point by 30°C or more. On a stock 4Runner that's a slow-degradation issue. On a heavy 4Runner running 33s or doing long downhill grades in 4Lo, that water turns to vapor under sustained braking and your pedal goes to the floor. This is the failure mode behind most "my brakes disappeared" complaints on Tacoma World, IH8MUD, and the 4Runner forums.
Toyota specifies DOT 3 from the factory and the fill cap says so. DOT 4 is compatible and has a higher dry boiling point, which makes it the right choice for a rig that does long descents or runs big tires. DOT 5.1 is also glycol-based and compatible with DOT 3/4. The only fluid you must never use is DOT 5 — that's silicone-based, will not mix with DOT 3/4, and will destroy the ABS unit. The bottles look similar; read the label.
Capacity for a full flush is 1 quart on a 4th gen (2003–2009) and 1–1.5 quarts on a 5th gen (2010–2024) because the longer brake lines hold more fluid. Buy two quarts. You'll use about 1.2 quarts for the flush and keep the second for top-offs over the next year. Always use a fresh, sealed container — opened brake fluid begins absorbing water immediately and is suspect after 12 months on a shelf.
Order of bleeding is farthest from master cylinder to nearest: right rear, left rear, right front, left front. The 5th gen's ABS/VSC system holds fluid in the modulator and won't fully flush from a bench bleed — for a complete flush, Toyota Techstream or a service tool that cycles the ABS pump is recommended, but for a routine fluid swap the standard four-corner bleed is sufficient. Watch the reservoir level constantly — if it runs dry you've sucked air into the master cylinder and the job doubled in length.
| Part | Vendor | Est. price |
|---|---|---|
| Genuine Toyota DOT 3 brake fluid (1 qt) | Toyota | ~$12 |
| Valvoline DOT 3/4 brake fluid (32 oz) | Valvoline | ~$10 |
| Motul DOT 5.1 brake fluid (1L) | Motul | ~$22 |
| Mityvac vacuum bleeder kit | Mityvac | ~$55 |
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.