The 4.0L takes 6 quarts and the 4.7L takes 6 quarts — both run 5W-30 for daily use, and both are quick driveway jobs once the truck is level and on stands.
The WJ's two engines share an oil capacity (6 quarts including filter) and a recommended weight (5W-30 for most climates, 10W-30 if you live somewhere hot and the engine is high-mileage). What's different is the filter location and the sensitivity to the wrong filter on the 4.7L. The 4.7L PowerTech is known for sludge problems, and a marginal filter contributes — stick to Mopar 5281090AB or a known-good equivalent (WIX 51068, Fram Ultra XG10575) on the 4.7. The 4.0L is more forgiving but you still want a real filter, not a generic.
Park on level ground and warm the engine for 5 minutes so the oil flows. Lift the front with a floor jack at the front crossmember and set it on jack stands rated for the truck's weight (the WJ is heavier than it looks at around 4,200 lbs). Position the drain pan under the oil pan. The drain plug uses a 13mm socket on both engines. Crack it loose, then back it out by hand the last few turns so it doesn't drop into the pan.
Filter location: 4.0L is on the driver-side rear of the engine block, accessible from below. 4.7L is on the driver-side front, also from below but trickier — there's not much clearance. An oil filter wrench helps both. Hand-tighten the new filter (oil the gasket first), then snug it a quarter-turn past contact. Don't gorilla it on.
Refill from the top with 6 quarts, run for 30 seconds, check the dipstick, top off as needed. Reset the oil indicator if your model has one (most pre-2003 WJs don't — they want you to remember).
| Part | Vendor | Est. price |
|---|---|---|
| Mopar oil filter (4.0L) | Mopar | ~$8 |
| Mopar 4.7L H.O. oil filter | Mopar | ~$12 |
| 5W-30 conventional motor oil (6 qt) | Valvoline / Mobil / Pennzoil | ~$25 |
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.