Single belt drives water pump, alternator, PS, and A/C. Spring-loaded tensioner; routine inspection for cracks every oil change.
From 1991 onward the 4.0L runs a single serpentine belt with a spring-loaded automatic tensioner. Renix-era (1987-1990) uses multiple V-belts (see separate entry). For the serpentine, the routing diagram is on a sticker on the radiator support; if missing, the belt wraps the crank, idler, water pump, alternator, power steering, and A/C if equipped. Tensioner pulley takes a 15mm or 1/2 drive square to release. The OE Gates K060923 (no A/C) or K060935 (with A/C) length covers most 4.0L XJ applications - verify on your specific routing. Look for cracks across multiple ribs, glazing, or chunking. A 'whine' usually means a tensioner pulley bearing rather than the belt; a 'chirp' is more often the belt itself. Plan to replace the tensioner around 100k miles - the internal spring loses tension and the belt will start slipping under load (visible at A/C compressor engagement).
| Part | Vendor | Est. price |
|---|---|---|
| Gates serpentine belt (with A/C) | RockAuto | ~$25 |
| Belt tensioner assembly | Mopar/Dayco | ~$40 |
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.