The serpentine belt drives every accessory on the 4.0L — alternator, power steering, water pump, and A/C — and replacing it is a thirty-minute job that almost any XJ owner can handle with one breaker bar and a flashlight. Do it every 60,000 miles or sooner if you see cracks, glazing, or hear squeal on cold starts.
A failed belt strands you. When it breaks, the alternator stops charging, power steering goes dead, and the water pump quits circulating coolant — you have minutes before the engine overheats. The good news is that belts give warning. Cracks across the ribs, chunks missing from the rib tips, a glossy glazed surface, or a high-pitched squeal on cold mornings all mean the belt is overdue. Inspect at every oil change, replace at the first sign of degradation, and you'll never deal with a roadside failure.
While the belt is off, check the tensioner and idler pulleys. The tensioner is a spring-loaded arm that keeps constant tension on the belt — when its spring weakens with age (usually around 100,000 miles), the belt slips under load and squeals. The idler pulley is a plain bearing wheel that the belt rides over; when its bearing fails it whines, vibrates, or seizes. Both are inexpensive to replace and most owners do all three components together once the belt is off.
The belt routing differs between 4.0L XJs with and without A/C, so confirm which version you have before buying parts. Most 1991-2001 XJs came with A/C from the factory.
Why it works
Restores reliable charging, power steering, and cooling in one inexpensive job. A worn belt is the cheapest single point of failure to fix on the 4.0L.
Replacing the tensioner and idler pulley with the belt while everything is off prevents a future second job. The tensioner is the most common reason a "new" belt squeals or wears prematurely.
No fluids, no specialty tools, no disassembly beyond loosening the tensioner. This is the perfect first wrenching job for a new XJ owner — it builds confidence with engine-bay routing and pulley inspection.
Trade-offs
The radiator fan and shroud make working around the belt cramped. Reaching the tensioner means working blind around the fan; expect knuckle-scrape risk. A long-handle breaker bar makes a noticeable difference over a short ratchet.
The wrong belt length will not let the tensioner sit in its operating range, and the part-counter cross-reference is occasionally wrong for A/C-delete or aftermarket-pulley XJs. Bring the old belt to the store and confirm length before walking out.
A tensioner that has been weak for years can mask other problems. If the new belt still chirps after installation, the next step is a new tensioner — assume the spring is the culprit rather than the new belt.
Tools required
1/2-inch drive breaker bar or long ratchet
15mm socket (some tensioners) or 1/2-inch square drive directly into tensioner
flashlight
phone or camera for routing photo
shop rag
Parts
Part
Vendor
Est. price
Serpentine Belt — 4.0L with A/C (6-rib, ~89.5 in)
Gates
~$22
Serpentine Belt — 4.0L without A/C (6-rib, ~84.5 in)
Gates
~$20
Belt Tensioner Assembly (4.0L, 1991-2001)
Gates
~$55
Idler Pulley (4.0L)
Gates
~$28
Sources
{'title': 'Gates Belt Cross-Reference — Jeep Cherokee 4.0L', 'url': 'https://www.gates.com/us/en/power-transmission/automotive-belts/k060895.html'}
{'title': 'NAXJA — Serpentine Belt Routing Diagram and Tensioner Tips', 'url': 'https://www.naxja.org/forum/showthread.php?t=120451'}
{'title': 'Cherokee Forum — Tensioner Replacement Walkthrough', 'url': 'https://www.cherokeeforum.com/f2/serpentine-belt-tensioner-replacement-186324/'}
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.