2015 Ram 2500 — Spark Plug Type, Gap & Torque

Quick reference

Note: 5.7L and 6.4L HEMI engines use 16 spark plugs (two per cylinder). Always verify plug quantity before ordering.

Why the right plug matters

• Heat range: The HEMI’s combustion chambers run hot under load. A correct heat range avoids pre-ignition (too hot) and fouling (too cold). Factory calibration is designed around the OE heat range—don’t deviate unless a calibrated tuner or engine builder specifies it.
• Electrode material:
  • Copper/nickel: Excellent conductivity and strong spark, but faster wear. That’s why these HEMIs call for ~30k-mile service intervals.
  • Platinum: Longer life than copper with modest cost. Suitable for extended intervals, though not typically the factory spec on HD HEMIs.
  • Iridium: Very long life and stable gap over time. Quality iridium plugs can stretch intervals near 100k miles in light-duty use. If you choose iridium on a truck that tows/hauls frequently, inspect sooner.

How to gap a spark plug

• Use a wire-style or feeler gauge tool to measure. Disk-style tools can be okay but can stress fine-wire electrodes.
• Factory iridium/platinum fine-wire plugs often come pre-gapped—verify the gap, don’t force it. For the HEMI target 0.043 in (1.10 mm) unless a calibration specifies otherwise.
• To adjust, bend only the ground strap with a light touch; never pry against the center electrode or iridium tip.
• Re-check after any adjustment. Consistency across all cylinders matters for smooth idle and balanced ignition load.

Replacement procedure tips (2015 Ram 2500 HEMI)

These HEMIs use a coil-near-plug setup with eight ignition coils and short secondary leads to the twin plugs—there are 16 plugs total.

• Access and labeling:
  • Work on a cool engine to protect the aluminum heads and avoid seized threads.
  • Remove engine covers as needed. Unplug one coil at a time to keep routing tidy. Label the short plug wires so each returns to its cylinder.
• Coil and boot care:
  • Remove the 8mm (varies) coil hold-down bolt, then twist the boot to release the seal before pulling straight out.
  • Inspect boots and short leads for oil or coolant contamination; replace any swollen or cracked boots.
• Plug removal:
  • Blow out each well with compressed air to keep debris out of the cylinder.
  • Use a proper spark plug socket and a small extension. Break each plug loose, then back it out by hand.
• Thread preparation and anti-seize:
  • OE and NGK/Denso shells are nickel-plated—install dry. Anti-seize lowers friction and can lead to over-torque and thread damage. If anti-seize is used against recommendation, reduce torque by roughly 20–30%.
• Installation:
  • Verify gap (0.043 in / 1.10 mm). Start each plug by hand; you should get several turns of smooth engagement.
  • Torque to 13 lb-ft (18 Nm) on clean, dry threads in the aluminum heads.
  • Apply a small amount of dielectric grease inside each coil boot and short plug-wire boot to aid sealing and future removal.
  • Reinstall coils/wires, reconnect electrical connectors, and clear any stored misfire codes after the job.

Known issues

• No two-piece Ford 3-valve plugs: The 5.7L/6.4L HEMI does not use the problematic two-piece plug design from certain Ford 3-valve V8s, so specialized extraction procedures are not required here.
• Not a GM ion-sensing system: The HEMI ignition does not use GM’s ionization-sensing coils, so misfire diagnostics are conventional.
• Common HEMI service notes:
  • Stuck boots or torn short leads are common on high-mileage engines—plan on replacing boots/wires as needed.
  • Cross-threading and over-torque are the biggest failure modes. Always start by hand and torque accurately.
  • Occasional water intrusion into plug wells (after deep washes or heavy rain) can cause temporary misfires—dielectric grease on boots helps seal.

If you’re unsure of the exact Mopar plug part number, check the Mopar EPC by VIN or consult a dealer; Chrysler supersedes plug part numbers periodically and HD applications may differ from light-duty specs.

Need plugs replaced? Find a shop on Repairius.