2015 Ram 3500 Spark Plug Type & Gap

Quick reference

Why the right plug matters

Choosing the correct spark plug for your 2015 Ram 3500 is more critical than you might think. Spark plugs are not a "one-size-fits-all" component; each engine is designed to operate optimally with a specific plug type, heat range, and gap. Using the wrong plug can lead to a host of problems, from reduced fuel economy and diminished performance to misfires and even serious engine damage.

Heat Range

The "heat range" of a spark plug refers to its ability to dissipate heat from the combustion chamber. A "cold" plug dissipates heat more quickly, while a "hot" plug retains more heat. Using a plug that 's too hot can lead to pre-ignition and detonation, which are extremely harmful to an engine. Conversely, a plug that 's too cold can cause fouling, where carbon deposits build up on the plug, leading to misfires. Your Ram 3500 's engine is designed for a specific heat range, and the OEM recommended plugs are engineered to meet this requirement.

Electrode Metal (Iridium vs. Platinum vs. Copper)

• Copper: These are the most basic and oldest spark plug design. Copper has excellent electrical conductivity but a softer electrode that wears down relatively quickly. They are typically found in older vehicles or those with high-performance applications where frequent changes are expected. The 5.7L Hemi in your Ram 3500 utilizes a copper-tipped plug for optimal performance and longevity at its specified interval.

• Platinum: Platinum plugs offer better durability than copper, thanks to platinum 's higher melting point. They typically last longer than copper plugs and are often found in vehicles with longer service intervals. They provide a good balance of performance and longevity.

• Iridium: Iridium is one of the hardest and most corrosion-resistant metals used in spark plugs. Iridium plugs have extremely fine electrodes, which allows for a more focused and efficient spark. This translates to improved fuel economy, smoother idle, and extended service life, often exceeding 100,000 miles. The 6.4L Hemi in your Ram 3500 uses iridium plugs, contributing to its longer service interval.

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 for copper plugs. An incorrect gap can lead to misfires, poor fuel economy, and reduced engine performance.

To gap a spark plug, you 'll need a spark plug gap gauge (either a wire-type or a ramp-style tool). Gently widening or closing the gap should be done with care to avoid damaging the electrode. For wire gauges, you can gently bend the ground electrode to achieve the correct gap. For ramp-style gauges, you 'll slide the plug along the ramp until it reaches the desired measurement. Always be gentle and avoid putting pressure on the center electrode.

Replacement procedure tips

Replacing spark plugs on your 2015 Ram 3500, especially with the coil-on-plug (COP) ignition system, requires a methodical approach. The 5.7L and 6.4L Hemi engines feature individual ignition coils mounted directly on top of each spark plug, eliminating the need for traditional spark plug wires.

1. Preparation: Ensure the engine is cool to the touch. This prevents potential damage to the cylinder head threads and reduces the risk of burns. Disconnect the negative battery terminal.

2. Coil-on-Plug Removal: Carefully disconnect the electrical connector from each ignition coil. Then, unbolt the coil (usually a single bolt) and gently twist and pull upward to remove it. Avoid yanking on the coil or the electrical connector.

3. Cleanliness is Key: Before removing the old spark plugs, use compressed air to blow away any debris around the spark plug wells. This prevents dirt and grime from falling into the combustion chamber once the old plug is removed.

4. Spark Plug Removal: Use a spark plug socket with a rubber insert to carefully remove the old plugs. The rubber insert helps to prevent the plug 's ceramic insulator from cracking. Turn counter-clockwise to loosen.

5. Anti-Seize Debate: There 's ongoing debate about using anti-seize on spark plug threads. For spark plugs with nickel-plated shells (common with many OEM and aftermarket plugs for modern engines), manufacturers often advise against using anti-seize. The nickel plating provides adequate anti-seize properties, and adding more can lead to over-torquing and potential damage to the cylinder head threads. Refer to the spark plug manufacturer 's recommendations. If you do use anti-seize, use it sparingly and reduce the torque specification by approximately 10-20%.

6. Dielectric Grease on Boots: Apply a thin layer of dielectric grease to the inside of the spark plug boot (the part of the ignition coil that connects to the spark plug). This helps to seal out moisture, prevents corrosion, and makes future removal easier.

7. Installation: Hand-thread the new spark plugs into the cylinder head to avoid cross-threading. Once finger-tight, use a torque wrench to tighten them to the manufacturer 's specified torque. Overtightening can damage the spark plug and cylinder head threads; undertightening can lead to misfires and poor sealing.

8. Reassembly: Reinstall the ignition coils, securing them with their bolts and reconnecting the electrical connectors. Reconnect the negative battery terminal.

Known issues

Fortunately, the 2015 Ram 3500 with either the 5.7L or 6.4L Hemi engines does not have widespread, notorious spark plug issues like some other manufacturers (e.g., the Ford 3-valve engine 's two-piece spark plug breakage). As long as you use the correct spark plugs and adhere to the recommended replacement intervals and procedures, you should experience trouble-free operation.

Need plugs replaced? Find a shop on Repairius.