The Gladiator's 3.6L Pentastar has six cylinders arranged in a V configuration — three on each bank. Stellantis recommends spark plug replacement at 60,000 miles. In practice, iridium plugs often go longer; copper plugs need replacement closer to 30,000 miles if the JT does significant idling or towing.
The 3.6L Pentastar is a well-proven engine but the V6 layout means the rear bank (cylinders 4, 5, 6) is significantly harder to access than the front bank. Budget extra time for the rear plugs — they require working over the top of the engine near the firewall, and a ratchet with a universal joint or swivel extension makes the job manageable without skinning knuckles. A spark plug socket with a rubber insert (to grip the plug during extraction) is mandatory — dropping a plug down into the cylinder head on the rear bank is a very bad day.
**Factory plug specification:** The JT 3.6L uses a 14mm thread, 5/8" socket plug gapped at 0.042". Confirm with your NGK or Denso application guide before purchasing — plug length matters and an incorrect plug depth can cause pre-ignition damage.
Champion Platinum set of 6: ~$35. Adequate for normal use, shorter service life than iridium.
NGK Iridium IX set of 6: ~$48. The right choice for most JT owners — iridium lasts longer, fires more consistently, and the price premium over copper pays back in extended interval.
Denso Iridium TT set of 6: ~$58. Slightly better electrode design than standard iridium — minimal real-world difference from NGK Iridium on a naturally aspirated street/trail JT.
Mopar OEM set of 6: ~$65. Factory-spec iridium, carries a Mopar warranty. No performance benefit over NGK or Denso iridium — the premium is the brand.
Shop labor for spark plug replacement on a V6 (accessible bank + rear bank): ~$200–300. The rear bank access is what shops charge for — it's legitimate labor time. If you're comfortable with the task, the DIY save is real.
| Part | Vendor | Est. price |
|---|---|---|
| NGK Iridium IX Spark Plugs — 3.6L Pentastar (set of 6) | NGK | ~$48 |
| Champion Platinum Power Spark Plugs — 3.6L (set of 6) | Champion | ~$35 |
| Mopar OEM Spark Plugs — Gladiator JT 3.6L (set of 6) | Mopar | ~$65 |
| Denso Iridium TT Spark Plugs — 3.6L Pentastar (set of 6) | Denso | ~$58 |
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.