2018 Ram 3500 Spark Plug Type & Gap

Quick Reference

Why the right plug matters

Choosing the correct spark plug for your 2018 Ram 3500 is crucial for optimal engine performance, fuel efficiency, and longevity. Spark plugs ignite the air-fuel mixture in your engine's cylinders, and the wrong plug can lead to misfires, reduced power, and even engine damage.

Heat Range

Spark plugs are designed with a specific "heat range" that dictates how quickly they dissipate heat from the combustion chamber. A "hot" plug retains more heat, while a "cold" plug dissipates heat more quickly. Using a plug with an incorrect heat range can lead to pre-ignition (where the fuel ignites before the spark) or fouling (where carbon deposits build up on the plug).

Electrode Metal: Iridium vs. Platinum vs. Copper

• Copper: Copper spark plugs are the most common and typically the least expensive. They have excellent conductivity and are often used in older vehicles or those with shorter recommended replacement intervals, such as the Hemi engines in your Ram 3500. They usually require replacement around 30,000 miles.

• Platinum: Platinum plugs offer better durability and a longer lifespan than copper plugs, often lasting 60,000 to 100,000 miles. They are more expensive but can be a good investment for extended service intervals.

• Iridium: Iridium plugs are the most durable and highest-performing option. They feature a very fine electrode, which provides a more consistent and powerful spark. Iridium plugs can last 100,000 miles or more and are often found in modern, high-performance engines.

For your 2018 Ram 3500 with either the 5.7L or 6.4L Hemi engine, the OEM recommendation is typically a copper core plug, necessitating a 30,000-mile replacement interval. While you can use platinum or iridium plugs, you won't see a significant performance benefit, and the cost might not be justified for the recommended service interval.

How to gap a spark plug

Properly gapping a spark plug is essential for a strong spark and efficient combustion. The gap is the distance between the center electrode and the ground electrode. For your 2018 Ram 3500, the recommended gap is 0.043 inches (1.1 mm).

To gap a spark plug, you'll need a spark plug gap tool (a coin-style or wire-style gauge). Gently slide the wire gauge of the correct thickness between the electrodes. If the gap is too small, use the tool's gapping lever to gently bend the ground electrode outward. If the gap is too large, carefully tap the ground electrode on a hard surface to close the gap slightly. Always be gentle to avoid damaging the electrode.

Note: Many modern spark plugs, especially platinum and iridium, come pre-gapped from the factory. It's always a good idea to double-check the gap, but only adjust if absolutely necessary and with extreme care.

Replacement procedure tips

Replacing spark plugs on your 2018 Ram 3500 with a Hemi engine is a straightforward process, but a few tips can make it smoother.

1. Coil-on-Plug Removal: Both the 5.7L and 6.4L Hemi engines use a coil-on-plug (COP) ignition system. Each spark plug has its own ignition coil mounted directly on top of it. To access the plugs, you'll need to disconnect the electrical connector from each coil and then remove the coil hold-down bolt (usually a 10mm or similar bolt). Gently pull the coil straight up to remove it.

2. Anti-Seize Debate: There's ongoing debate about whether to use anti-seize compound on spark plug threads. Mopar (and some spark plug manufacturers like NGK) often advise against using anti-seize on modern spark plugs with nickel-plated shells, as it can alter torque readings and lead to over-tightening. If you choose to use it, apply a very thin layer and reduce your torque spec by about 20%. Our recommendation is to follow the manufacturer's guidelines – if the plugs are nickel-plated, anti-seize is generally not needed.

3. Dielectric Grease on Boots: Applying a small amount of dielectric grease inside the spark plug boot (the end that connects to the spark plug porcelain) can help prevent moisture intrusion and make future removal easier. Be careful not to get any grease on the electrode tips.

4. One at a Time: To avoid mixing up spark plug wires or coils, it's best to replace one spark plug at a time. Remove the coil, remove the old plug, install the new plug, re-install the coil, and then move to the next cylinder.

Known issues

Fortunately, the Hemi engines in the 2018 Ram 3500 are not known for common spark plug-related issues like the Ford 3-valve engine's broken 2-piece plugs. However, consistently neglecting spark plug replacement can lead to misfires, reduced fuel economy, and potentially premature wear on ignition coils.

Need plugs replaced? Find a shop on Repairius.