Replace all six iridium plugs every 100,000 miles. Torque to 13 ft-lb (17.5 N·m) — the 12mm Pentastar plugs strip if you over-tighten. Plan on an hour in the driveway.
The 3.6L Pentastar in the JL uses 12mm spark plugs — smaller than the 14mm plugs in older Jeep engines. That matters for two reasons. First, the spark plug socket is 5/8" (16mm), not the 13/16" that fits the 4.0L. Second, the thinner shell strips its threads at much lower torque, so a regular click-type torque wrench set to "feel" is not good enough. Use a wrench that reads in inch-pounds or one that goes down to single-digit foot-pounds.
NGK ILKAR7L11 is the direct factory equivalent and runs about $55 for a set of six. Mopar's branded plug is the same NGK part with a Chrysler box and a markup. There is no benefit to going up a heat range or to a one-step-colder plug on a stock motor — the OEM iridium plugs are correct for stock and lightly modified Pentastars. Skip the anti-seize; NGK explicitly says not to use it on iridium plugs, and the plated threads do not need it.
Access on the JL is straightforward. The coil packs sit on top of each cylinder, held by a single 10mm bolt. Remove the bolt, twist the coil to break the rubber boot seal, lift it off, and you are looking at the plug well. Use a 6-inch extension and the 5/8" plug socket. The plug well is deep — a magnetic or rubber-insert socket keeps the old plug from dropping into the head when you back it out.
Reinstall each new plug by hand first to confirm thread engagement — never start a plug with a ratchet. Torque to 13 ft-lb (17.5 N·m). A dab of dielectric grease inside the coil boot helps it pull off cleanly the next time. Reinstall the coil with the 10mm bolt, repeat for the remaining five cylinders. Total job time is about an hour the first time, 30 minutes after that.
Symptoms that mean it is time: rough idle at startup, misfire code (P0301–P0306), or a noticeable loss of low-end response. Most JLs make it to the 100,000-mile interval cleanly. Track-driven or extreme cold-climate Jeeps benefit from inspecting at 75,000.
| Part | Vendor | Est. price |
|---|---|---|
| NGK Laser Iridium ILKAR7L11 (set of 6) | NGK | ~$55 |
| Mopar OEM spark plug (set of 6) | Mopar | ~$75 |
| Dielectric grease (small tube) | Permatex | ~$4 |
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.