2021 Ram 2500 Spark Plug Type & Gap

Quick reference

Why the right plug matters

Choosing the correct spark plug for your 2021 Ram 2500 is crucial for optimal engine performance, fuel efficiency, and longevity. Using the wrong plug can lead to misfires, reduced power, poor fuel economy, and even costly engine damage. There are several key factors that differentiate spark plugs:

• Heat Range: This refers to the plug's ability to dissipate heat from the combustion chamber. A "hot" plug retains more heat, while a "cold" plug dissipates it faster. The correct heat range is determined by the engine manufacturer and is essential for preventing pre-ignition (too hot) or fouling (too cold). The 6.4L HEMI uses a specific heat range optimized for its performance characteristics.
• Electrode Material: This significantly impacts the plug's lifespan and performance.
  • Iridium: These plugs, like the NGK LFR6AIX-11 or Denso IKH20TT, offer the longest lifespan and best performance. Iridium is extremely hard and allows for a very fine electrode tip, concentrating the spark for more efficient combustion. This is the OEM-recommended type for your 2021 Ram 2500 6.4L HEMI.
  • Platinum: While not OEM for your application, platinum plugs offer a good balance of performance and longevity, typically lasting longer than copper plugs.
  • Copper: These are the most common and least expensive but have the shortest lifespan. They are generally not recommended for modern engines like the 6.4L HEMI due to their inability to withstand the higher voltage and temperatures for extended periods.

How to gap a spark plug

While many iridium plugs come pre-gapped, it's always a good practice to double-check the gap before installation. The correct gap for your 2021 Ram 2500 6.4L HEMI is 0.043 inches (1.1 mm). To gap a spark plug:

1. Use the Right Tool: A wire-type spark plug gapping tool or a feeler gauge is recommended. Avoid coin-style gappers, as they can damage the fine electrode of iridium plugs.
2. Check the Gap: Slide the appropriate gauge wire or feeler blade between the center and ground electrodes. It should slide through with slight drag.
3. Adjust if Necessary: If the gap is too small, carefully bend the ground electrode outwards using the gapping tool's adjustment slot. If the gap is too wide, gently tap the ground electrode on a clean, hard surface to close it.
   • Important: Never apply pressure or bend the center electrode, especially on iridium plugs, as it can easily break the delicate tip.

Replacement procedure tips

Replacing spark plugs on your 2021 Ram 2500 6.4L HEMI can be a rewarding DIY task, but careful attention to detail is key.

• Coil-on-Plug Removal: The 6.4L HEMI utilizes a coil-on-plug setup. To remove the ignition coils, carefully disconnect the electrical connector by pressing the release tab and pulling. Then, gently twist and pull the coil straight up to remove it from the spark plug well. Avoid yanking on the wires.
• Anti-Seize Debate: There's ongoing debate about using anti-seize on spark plug threads. Most modern spark plugs, especially those with nickel-plated shells, do not require anti-seize. The manufacturer's torque specifications are typically for clean, dry threads. Applying anti-seize can act as a lubricant, causing over-tightening and potentially stripping the cylinder head threads or breaking the plug. For your 2021 Ram 2500 6.4L HEMI, it is generally recommended not to use anti-seize. If you choose to use it, reduce the torque specification by 10-20% and use a very thin coating.
• Dielectric Grease on Boots: A small amount of dielectric grease applied to the inside of the spark plug boot (where it contacts the ceramic insulator) can help prevent sticking and corrosion, making future removal easier and improving electrical insulation. Do not put dielectric grease on the spark plug electrode tips.
• Torque Wrench is Crucial: Always use a calibrated torque wrench when installing new spark plugs. The specified torque for your 6.4L HEMI is 13 lb-ft (18 Nm). Under-tightening can lead to combustion gas leakage and plug overheating, while over-tightening can strip threads in the cylinder head or crack the spark plug insulator.
• One at a Time: To avoid mixing up spark plug wires or coils, replace one spark plug at a time, from start to finish.

Known issues

Fortunately, the 6.4L HEMI engine in the 2021 Ram 2500 does not have widespread, notorious spark plug-related issues like the Ford 3-valve engine