2022 GMC Sierra 2500HD Spark Plug Type & Gap

Quick reference

Why the right plug matters

Choosing the correct spark plug for your 2022 GMC Sierra 2500HD is crucial for optimal engine performance, fuel efficiency, and emissions. Spark plugs are designed with a specific "heat range" – a measure of how quickly the plug dissipates heat from the combustion chamber. A plug that's too hot can lead to pre-ignition and detonation, damaging engine components. A plug that's too cold can foul more easily, leading to misfires and poor performance.

Modern engines, like the 6.6L L8T in your Sierra, are typically designed for iridium or platinum spark plugs. These "precious metal" plugs offer significantly longer service intervals compared to traditional copper plugs due to their superior durability and resistance to wear. Iridium, being harder and having a higher melting point than platinum, allows for even finer electrodes, which results in a more concentrated spark and improved ignitability. While copper plugs are excellent conductors, their softer electrode material wears down much faster, making them unsuitable for the extended service intervals of modern engines. Using an incorrect plug material or heat range can negatively impact your engine's performance and longevity.

How to gap a spark plug

While many modern iridium and platinum spark plugs come pre-gapped, it's always a good practice to double-check the gap before installation. For your 2022 GMC Sierra 2500HD 6.6L V8, the recommended spark plug gap is 0.040 inches (1.0 mm). Always refer to the manufacturer's specifications, as an incorrect gap can lead to misfires, reduced fuel economy, and even engine damage.

To gap a spark plug, you'll need a wire-type gap gauge. Avoid using flat disc-style gauges on fine-wire iridium or platinum plugs, as they can damage the delicate electrode. Gently slide the appropriate wire thickness of the gauge between the center and ground electrodes. If the gap is too small, carefully bend the ground electrode outwards with the gapping tool. If the gap is too wide, gently tap the ground electrode on a hard, non-abrasive surface to close the gap. Always make small adjustments and re-check until the desired gap is achieved.

Replacement procedure tips

Replacing spark plugs on your 2022 GMC Sierra 2500HD 6.6L V8 is a straightforward procedure for the mechanically inclined, thanks to its coil-on-plug ignition system. This system eliminates traditional spark plug wires, with each spark plug having its own ignition coil mounted directly on top of it. Here are some tips for a smooth replacement:

1. Safety First: Ensure the engine is cool before starting. Disconnect the negative battery terminal to prevent accidental electrical issues.
2. Access: You may need to remove engine covers or air intake components to gain full access to all the ignition coils and spark plugs.
3. Coil-on-Plug Removal: Disconnect the electrical connector from each ignition coil. Carefully unbolt and remove the coil. Sometimes a slight twisting motion helps free the coil from the spark plug.
4. Cleaning: Before removing the old spark plugs, use compressed air to blow away any dirt or debris around the spark plug wells. This prevents contaminants from falling into the combustion chamber once the old plug is removed.
5. Anti-Seize Debate: There's ongoing debate regarding the use of anti-seize on spark plug threads. For spark plugs with nickel-plated shells, like the recommended ACDelco plugs, anti-seize is generally not necessary and can even lead to over-torquing. GM specifically recommends not using anti-seize with their factory plugs to avoid skewing torque readings and potential stripped threads. Most spark plug manufacturers also advise against it. If you choose to use it, apply it sparingly and reduce the torque specification by approximately 10-20%.
6. Dielectric Grease: Apply a small amount of dielectric grease inside the spark plug boot (the end of the ignition coil that connects to the spark plug). This helps seal out moisture, prevents corrosion, and makes future removal easier. Be careful not to apply it to the electrode tip.
7. Torque: Always use a torque wrench to tighten the new spark plugs to the specified 11 lb-ft (15 Nm). Over-tightening can damage the spark plug or cylinder head threads, while under-tightening can lead to combustion gas leaks and misfires. Remember the 10-20% reduction if you opt for anti-seize.

Known issues

Fortunately, the 6.6L V8 L8T engine in the 2022 GMC Sierra 2500HD is not widely known for specific spark plug related issues such as cracked porcelain or broken plug shells that plagued some earlier Ford or GM engines. The coil-on-plug design is robust, and as long as the correct spark plugs are used and replaced at the recommended interval, you should experience reliable ignition performance.

Need plugs replaced? Find a shop on Repairius.