2018 Ram 2500 Spark Plug Type & Gap

Quick reference

Why the right plug matters

Choosing the correct spark plug for your 2018 Ram 2500 is more critical than you might think. Spark plugs are not "one size fits all." Each engine is designed to operate within a specific thermal range, and the spark plug's heat range is crucial for maintaining this. A plug that is too "cold" can lead to fouling, while one that is too "hot" can cause pre-ignition and engine damage. The tip of the spark plug needs to be hot enough to burn off carbon deposits but not so hot that it becomes a source of ignition itself.

Electrode material also plays a significant role in performance and longevity. Most modern engines, including those in the 2018 Ram 2500, come with iridium or platinum plugs from the factory. These precious metals are incredibly durable and resistant to wear, allowing for much longer replacement intervals compared to traditional copper plugs. While copper plugs offer excellent conductivity and might be suitable for high-performance, frequently serviced applications, their lifespan is significantly shorter. Your Ram's Hemi engines are designed for the extended life and consistent performance that iridium or platinum plugs provide.

How to gap a spark plug

While many modern iridium and platinum spark plugs come pre-gapped from the factory, it's always a good practice to double-check the gap before installation, especially if you're using a copper or conventional plug. However, for iridium and platinum plugs, only adjust the gap if absolutely necessary and with extreme care. The fine-wire electrodes can be easily damaged.

To check the gap, use a wire-style or coin-style spark plug gap gauge. Gently slide the appropriate wire or edge of the gauge between the center and ground electrodes. There should be a slight drag. If adjustment is needed, use the bending tool on the gauge to gently bend the ground electrode. Never pry against the center electrode, as this can damage the insulator or the delicate electrode tip. For your 2018 Ram 2500, the specified gap for both the 5.7L and 6.4L Hemi engines is 0.043 inches (1.1 mm).

Replacement procedure tips

Replacing spark plugs on your 2018 Ram 2500's Hemi engine is a straightforward process, but a few tips can make it smoother:

• Coil-on-plug removal: Both the 5.7L and 6.4L Hemi engines use a coil-on-plug ignition system. Each spark plug has its own ignition coil mounted directly above it. To access the plugs, you'll need to disconnect the electrical connector from each coil and then remove the bolt (usually a 10mm) holding the coil in place. Gently twist and pull the coil straight up to remove it. Avoid yanking on the electrical connector.
• Anti-seize debate: There's ongoing debate about using anti-seize on spark plug threads. Most modern spark plugs feature a special coating on the threads from the factory, making anti-seize unnecessary and potentially leading to over-torquing. If you do choose to use anti-seize, apply it sparingly and reduce the specified torque by about 10-20% to prevent over-tightening, which can lead to damaged threads or plug breakage. For Ram Hemi engines, it's generally recommended to install plugs dry and torque to spec.
• Dielectric grease on boots: Apply a small amount of dielectric grease inside the spark plug boot (the rubber part that connects to the top of the spark plug). This helps to seal out moisture, prevents corrosion, and makes future removal easier.

Known issues

Fortunately, the 2018 Ram 2500 with either the 5.7L or 6.4L Hemi engine does not have any widespread, well-documented spark plug-related "known issues" similar to the Ford 3-valve engine's propensity for broken two-piece plugs or the GM 5.3L's ionization-sensing coil problems. The Hemi engines are generally reliable concerning their ignition systems, provided proper maintenance and specified spark plugs are used.

Need plugs replaced? Find a shop on Repairius.