2015 GMC Sierra 2500HD Spark Plug Type & Gap

Quick reference

Why the right plug matters

Choosing the correct spark plug for your 2015 GMC Sierra 2500HD is crucial for optimal engine performance, fuel efficiency, and longevity. Spark plugs are not "one-size-fits-all" components; specific designs are engineered to complement your engine's unique characteristics.

Heat Range: The heat range refers to a spark plug's ability to dissipate heat from the combustion chamber. A plug that's too hot can lead to pre-ignition and detonation, damaging the engine. A plug that's too cold can cause fouling and misfires. OEM specifications ensure the correct heat range for your 6.0L LY6 V8 engine.

Electrode Metal: Modern engines like yours typically use iridium or platinum spark plugs due to their enhanced durability and extended service intervals.

• Iridium: Considered the best for modern applications, iridium plugs offer exceptional longevity and a fine-wire electrode for a more focused spark, leading to improved combustion and fuel efficiency. The 41-110 (ACDelco) and corresponding NGK/Denso plugs listed above are iridium.
• Platinum: Platinum plugs also provide excellent durability and a longer lifespan compared to traditional copper plugs. They are often used as an OEM alternative where iridium is not specified.
• Copper: While excellent conductors, copper plugs have a much shorter lifespan due to softer electrode material. They are rarely used in late-model vehicles due to their shorter service life.

How to gap a spark plug

While many iridium and platinum spark plugs come pre-gapped from the factory, it's always a good practice to double-check and adjust the gap if necessary, especially with aftermarket options. The 2015 GMC Sierra 2500HD 6.0L LY6 V8 requires a gap of 0.040 inches (1.02 mm).

Here's how to gap a spark plug:

1. Use a wire-type spark plug gapping tool: These tools provide accurate measurements and are less likely to damage the fine-wire electrodes of iridium or platinum plugs than tapered disc-style gauges.
2. Measure the gap: Carefully slide the appropriate wire gauge between the center and ground electrodes. It should slide with a slight drag.
3. Adjust if needed: If the gap is too small, gently bend the ground electrode outwards using the adjustment tool on your gapping tool. If the gap is too large, carefully tap the ground electrode on a hard surface to close the gap slightly. Never bend or pry on the center electrode, as this can damage the plug.
4. Re-verify: After any adjustment, re-measure the gap to ensure it's within specifications.

Replacement procedure tips

Replacing spark plugs on your 2015 GMC Sierra 2500HD 6.0L LY6 V8 is a manageable DIY task, but a few tips can make the process smoother and prevent potential issues.

1. Work on a cool engine: Always allow the engine to cool completely before attempting to remove spark plugs. Removing plugs from a hot aluminum cylinder head can strip the threads.
2. Coil-on-plug (COP) removal: Your engine utilizes a coil-on-plug ignition system. Each spark plug has its own ignition coil directly mounted above it.
   • Carefully disconnect the electrical connector from each coil by pressing the release tab.
   • Remove the single bolt securing each coil to the valve cover.
   • Gently twist and pull up on the coil assembly to remove it. The coil boot might be a bit stubborn; a slight rocking motion can help.
3. Anti-seize debate: There's ongoing discussion regarding the use of anti-seize compound on spark plug threads. For spark plugs with nickel-plated shells (like the recommended OEM ACDelco and aftermarket options), manufacturers generally advise against anti-seize. The plating prevents galling, and anti-seize can act as an electrical insulator, affecting proper torque readings and potentially leading to over-tightening. Follow the manufacturer's recommendation.
4. Dielectric grease on boots: Apply a small amount of dielectric grease (non-conductive) inside the spark plug boot (the end that connects to the plug). This helps lubricate the boot for easier installation and removal, and also helps seal out moisture, preventing misfires.
5. Torque specifications: Don't guess! Overtightening can strip threads, crack the plug's porcelain insulator, or damage the cylinder head. Under-tightening can lead to plugs backing out, causing misfires and potential damage. Use a torque wrench and adhere to the specified 11 lb-ft (15 Nm).
6. One at a time: Replace spark plugs one at a time to avoid mixing up ignition coil wiring.

Known issues

Fortunately, the 6.0L LY6 V8 engine in your 2015 GMC Sierra 2500HD does not have widely documented common spark plug issues like the infamous two-piece plugs found in some Ford 3-valve engines, or specialized ionization-sensing coils. Sticking to the OEM recommended iridium plugs and following proper installation procedures will generally ensure trouble-free operation.

Need plugs replaced? Find a shop on Repairius.