Both AMC engines in the CJ-7 take five quarts of 10W-30 or 15W-40, and both want a high-zinc (ZDDP) oil because the cam and lifters are flat-tappet — modern passenger car oils don't carry enough zinc to protect them.
The 258 inline-six and the 304 V8 share the same service approach. Drain pan under the pan, pull the drain plug, swap the filter, refill with five quarts. Where DIYers get into trouble is oil selection, not procedure: modern API SP oils have ZDDP capped at ~800 ppm to protect catalytic converters in newer engines. That cap is fine for a roller-cam motor and a problem for a flat-tappet AMC. Cam wipe is the failure mode — and it shows up as a flat lobe a season later, not the day you change the oil.
The fix is to run a high-ZDDP oil. Diesel-rated 15W-40 (Shell Rotella T4) is the cheap path and still carries ~1,200 ppm zinc. Valvoline VR1 Racing 10W-30 carries more (~1,400 ppm) and costs more. Either is correct. Avoid generic "high-mileage" oils — they're high in detergent, not zinc.
Filter sizing matters on the 258 specifically. The long-bodied Wix 51258 sits close to the driver-side engine mount. If the mounts are soft (and on a 40-year-old Jeep they often are), high drivetrain torque can let the engine flex enough to tag the filter. Inspect the mounts before you commit to a long filter. If they look cooked, install fresh mounts or run the shorter Wix 51522 — same threading, shorter can, more clearance.
The 304 V8 takes the Wix 51515 — a different filter entirely. Don't cross them.
Total capacity for both engines with a new filter is five quarts. Some shops recommend 5.5 quarts ("five plus a half for the filter") which lands the dipstick a hair above the full mark — fine, but the official spec is five.
| Part | Vendor | Est. price |
|---|---|---|
| Wix 51258 oil filter (AMC 258 I6) | Wix / NAPA Gold 1258 | ~$12 |
| Wix 51515 oil filter (AMC 304 V8) | Wix / NAPA Gold 1515 | ~$11 |
| Shell Rotella T4 15W-40 (high-ZDDP for flat-tappet cam) | Shell | ~$25 |
| Valvoline VR1 Racing 10W-30 (high-ZDDP, alternative) | Valvoline | ~$32 |
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.