One belt runs everything on the 1GR-FE — alternator, water pump, power steering pump, A/C compressor, and the fan. Replace it around 90,000-100,000 miles regardless of how it looks, because modern EPDM belts wear smooth instead of cracking and the visual inspection everyone relies on does not work anymore. The part is 90916-A2015 on a 2010-2024 truck, 99367-H2120 on a 2003-2009, about $35 either way, and an hour in the driveway. If it chirps, the tensioner is the more likely culprit than the belt.
There is no separate power steering belt on this platform. Some Toyota trucks split the accessory drive across two belts; the 4Runner's 4.0L V6 does not. One 6-rib serpentine wraps the crank, water pump, alternator, power steering pump, A/C compressor, an automatic tensioner, and two idlers. That single-belt architecture is the whole reason this job matters more than its price suggests — when the belt goes, you lose charging, steering assist, and coolant circulation at the same moment. On pavement that is a tow. Twenty miles up a Forest Service road it is a considerably worse afternoon.
Belts made before roughly 2005 used neoprene, which hardened and cracked across the ribs as it aged. You could look at one and know. EPDM belts — everything current, including the Toyota part — do not crack. They abrade, losing rib material a fraction of a millimeter at a time, and a belt with 40% of its material gone still looks glossy and intact to the naked eye.
Two things replace the old eyeball test:
Mileage. Plan on replacement at 90,000-100,000 miles. Under 60,000 miles a belt is almost never the problem. Over 120,000 miles it is overdue no matter how it presents.
A wear gauge. Gates and Continental both give away a small plastic go/no-go gauge that drops into the rib valleys. If it sits flush with the belt surface instead of standing proud, the ribs have worn past spec. Any parts counter that sells belts will hand you one.
Noise, read correctly. A chirp that appears on cold start and fades as the engine warms is a tensioner or misalignment signature far more often than a worn belt. A continuous squeal under electrical or steering load points at tension. Replacing the belt alone on a chirping truck is the most common wasted repair on this platform.
The automatic tensioner (Toyota 16620-31013 on the 1GR-FE) uses an internal spring and damper to hold constant tension as the belt stretches and the accessories load and unload. Two things fail in it: the spring weakens, and the pulley bearing dries out.
Test it with the belt off. Rotate the tensioner arm through its full travel with a breaker bar — it should move smoothly against firm, even spring pressure and return under control, not fall back. Spin the pulley by hand: it should be silent and free, with no grit, no wobble, and no side play at the arm pivot. Any roughness, any lateral rock, or a spring that feels soft means replace it.
At around $95 for the tensioner and $42-45 per idler, doing all three with the belt is roughly $220 in parts on a 150,000-mile truck. That is defensible preventive work on a vehicle you take away from pavement. On an 80,000-mile daily driver, belt only is the right call.
A 3/8 breaker bar (the tensioner arm on the 1GR-FE takes a square drive directly, so a dedicated serpentine tool is optional but makes the reach around the fan far less unpleasant), a metric socket set, a torque wrench for the tensioner and idler bolts, and a flashlight. Access on the 5th gen is tight between the fan shroud and the radiator — some people pull the shroud, most work around it. Photograph the routing before anything comes apart, and photograph it again from a second angle.
One pulley off in the routing. The classic mistake is running the belt on the wrong side of a smooth idler, which reverses the water pump. It will run, it will look almost right, and it will overheat. Your photo is the check.
A belt riding on an edge. If the new belt is not centered on a ribbed pulley, stop. That means a misrouted path or a misaligned accessory bracket, and it will shred the belt in short order — sometimes in miles.
Letting the tensioner slam. Controlled release, every time. A snapped-back tensioner can fail the internal damper immediately.
Chirp after a new belt. Do not replace the belt a second time. The remaining suspects, in order: tired tensioner, dry idler bearing, a misaligned pulley, or a contaminated belt surface from a coolant or power steering weep. Track down the leak before you install a third belt — see 4runner-power-steering-service if the fluid is coming from the front of the pump.
Overheating right after the job. If the temperature climbs after a belt change, shut it down and re-verify routing before doing anything else. Related reading: 4runner-water-pump and 4runner-cooling-service.
| Item | Cost |
|---|---|
| Toyota 90916-A2015 belt (2010-2024) | $35-42 |
| Toyota 99367-H2120 belt (2003-2009) | $32-38 |
| Gates or Bando aftermarket belt | $25-32 |
| Tensioner assembly 16620-31013 | $85-105 |
| Grooved idler 16603-31040 | $40-50 |
| Smooth idler 16604-31020 | $38-48 |
| Shop labor, belt only | $120-200 |
| Shop labor, belt plus tensioner and idlers | $350-500 |
Carrying a spare belt is worth the $30 if you travel remote. A serpentine belt is one of the few failures that can be limped past with a spare and hand tools on the trail, and it is the only single part whose failure takes out charging, steering assist, and cooling at once.
| Part | Vendor | Est. price |
|---|---|---|
| Toyota OEM Serpentine Belt (2010-2024 4.0L) | Toyota | ~$38 |
| Toyota OEM Serpentine Belt (2003-2009 4.0L) | Toyota | ~$35 |
| Toyota Belt Tensioner Assembly (1GR-FE) | Toyota / Aisin | ~$95 |
| Idler Pulley (grooved) | Toyota | ~$45 |
| Idler Pulley (smooth) | Toyota | ~$42 |
| Gates / Bando aftermarket 6-rib belt | Gates / Bando | ~$28 |
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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