Water Pump Replacement 4.0L

Difficulty: intermediate

Replacing the water pump on the 4.0L is a half-day job that prevents being stranded with an overheating engine. The most common mistake: ordering the wrong pump. Get the year right before you buy.

The XJ 4.0L water pump runs belt-driven off the front of the timing cover. It lasts 80,000–130,000 miles in most cases, but the bearing and shaft seal wear out before the impeller. When the seal goes, coolant weeps from a small drain hole on the underside of the pump housing — look for a dried orange or green crust below the pump and along the front of the engine. If you hear a low grinding growl from the front of the engine that changes with RPM and isn't the alternator, the bearing is on its way out.

**The part number trap.** The 1987–1990 Renix and 1991–2001 HO 4.0L use different water pumps with impellers pitched in opposite directions. They bolt on identically. Ordering the wrong one means the pump spins but moves coolant the wrong way — the engine overheats quickly and the impeller cavitates. Gates 42137 for Renix, Gates 41141 for HO. Confirm your year before you buy anything.

While the coolant is drained, replace the thermostat (it's a $10 part already in your hands) and inspect the bypass hose — the short rubber hose running from the pump inlet to the thermostat housing. On high-mileage XJs it's often original and cracks the moment you disturb it. Have a Dorman 56398 on hand. The thermostat housing on many XJs is plastic and prone to hairline cracks; Dorman makes a direct-fit aluminum replacement if yours looks suspect.

Why it works

Prevents roadside overheating — a failed water pump on the trail or highway is a major problem
Doing the thermostat and bypass hose at the same time costs almost nothing extra in labor
Gates and ACDelco pumps come with a new gasket included, keeping the job clean

Trade-offs

Wrong part number is a real risk — double-check year before ordering; Renix and HO pumps look identical
The bypass hose often tears on removal; budget $10 for the replacement
Cooling system air purging takes patience; rushing this step leads to mysterious overheating after the job

Tools required

Socket set (10mm, 13mm, 15mm)
Torque wrench
Serpentine belt tool or 15mm breaker bar (belt tensioner)
Drain pan (2-gallon minimum)
Plastic gasket scraper
Strap wrench or pulley holder (to hold pulley while loosening fan bolts)
Flathead screwdriver (hose clamps)

Parts

Part	Vendor	Est. price
Gates 41141 Water Pump (HO, 1991–2001)	RockAuto / Gates	—
Gates 42137 Water Pump (Renix, 1987–1990 — reverse rotation)	RockAuto / Gates	—
Thermostat 195°F (Stant 14328)	RockAuto / local	—
Bypass hose (Dorman 56398)	RockAuto / Dorman	—
Thermostat housing gasket	RockAuto / local	—

Sources

{'title': 'NAXJA — Water pump torque specs', 'url': 'https://naxja.org/threads/water-pump-torque-specs.1039807/'}
{'title': 'Cherokee Forum — Water pump replacement how-to', 'url': 'https://www.cherokeeforum.com/f51/waterpump-replacement-4-0-a-151476/'}
{'title': 'WAYALIFE — XJ 4.0L water pump, thermostat, fan clutch write-up', 'url': 'https://www.wayalife.com/threads/jeep-xj-cherokee-4-0l-water-pump-thermostat-fan-clutch-replacement-write-up.30583/'}

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.