2019 GMC Sierra 2500HD Spark Plug Type & Gap

Quick reference

Why the right plug matters

Choosing the correct spark plug for your 2019 GMC Sierra 2500HD is crucial for optimal engine performance, fuel efficiency, and longevity. The "right plug" refers to several key specifications:

• Heat Range: This dictates how well the spark plug dissipates heat from the combustion chamber. A plug that's too "cold" (dissipates heat too quickly) can lead to fouling, while a plug that's too "hot" (dissipates heat too slowly) can cause pre-ignition and engine damage. The OEM-specified heat range is engineered to match your engine's operating temperature and combustion characteristics.

• Electrode Metal: Modern engines, like those in your Sierra 2500HD, typically utilize long-life spark plugs made with precious metals:

  • Iridium: This is the most common material for modern OEM spark plugs due to its extreme hardness and high melting point. Iridium plugs feature very fine electrodes, which allows for a stronger, more consistent spark and extended service intervals (often 100,000 miles or more). The 6.0L L96 V8 in your Sierra 2500HD comes factory-equipped with iridium spark plugs.
  • Platinum: Platinum plugs also offer extended life compared to traditional copper plugs, though typically not as long as iridium. They often feature a platinum disc welded to the center electrode and/or ground electrode.
  • Copper: While excellent conductors, copper electrodes wear quickly, making them unsuitable for the long service intervals expected in modern vehicles. You will not find copper plugs as OEM in your 2019 Sierra 2500HD.

Using a plug with the incorrect heat range or electrode material can lead to misfires, reduced power, poor fuel economy, and premature plug wear.

How to gap a spark plug

While many iridium spark plugs come pre-gapped from the factory, it's always a good practice to verify the gap before installation, especially with aftermarket plugs. However, extreme caution is advised when gapping iridium or platinum plugs due to their delicate fine-wire electrodes. Improper gapping can easily damage the electrode, requiring a new plug.

For a 2019 GMC Sierra 2500HD 6.0L L96 V8, the gap is 0.040 in (1.0 mm).

1. Obtain the correct Gapping Tool: Use a wire-style or coin-style spark plug gap tool. Avoid using ramp-style gap tools, as they can damage fine-wire electrodes.
2. Measure the Current Gap: Carefully slide the appropriate wire gauge or the edge of the coin tool between the center and ground electrodes. There should be a slight drag.
3. Adjust (if necessary, with extreme care): If adjustment is needed, gently bend the ground electrode only. Never pry or bend the center electrode. For fine-wire plugs, it's often better to exchange a plug with an incorrect gap than to risk damaging it during adjustment.
4. Re-measure: Confirm the gap is correct after any adjustments.

Replacement procedure tips

Changing spark plugs on your 2019 GMC Sierra 2500HD 6.0L L96 V8 is a relatively straightforward job for a DIYer with the right tools and patience.

• Cool Engine: Always allow the engine to cool completely before attempting spark plug removal. This prevents potential thread damage to the cylinder heads, which are aluminum.
• Coil-on-Plug System: Your Sierra uses a coil-on-plug (COP) ignition system, meaning each spark plug has its own ignition coil mounted directly above it. To access the plugs, you'll need to:
  1. Disconnect the electrical connector from each coil. Press the tab and pull gently. Do not yank on the wires.
  2. Remove the bolt securing the coil to the valve cover (typically a 10mm bolt).
  3. Gently twist and pull up on the coil assembly to remove it. The spark plug boot may be snug.
• Anti-Seize Debate: There is ongoing debate about using anti-seize on spark plug threads. GM, like many manufacturers, has issued service bulletins advising against using anti-seize on spark plugs with factory-applied coatings (which most modern plugs have). The coating is designed to provide consistent torque readings and prevent seizing. Applying additional anti-seize can lead to over-torquing and potential damage to the cylinder head threads. It is generally recommended to follow the plug manufacturer's or vehicle manufacturer's recommendation. For ACDelco plugs, typically no anti-seize is needed.
• Dielectric Grease on Boots: A small amount of dielectric grease applied inside the spark plug boot (where it contacts the top of the spark plug ceramic) can help prevent the boot from sticking to the plug and aids in future removal. It also helps seal out moisture and improve electrical insulation.
• Torque Wrench is Crucial: The specified torque for your 6.0L L96 V8 spark plugs is quite low: 11 lb-ft (15 Nm). Using a calibrated torque wrench is essential to prevent over-tightening (which can damage the cylinder head threads) or under-tightening (which can lead to loose plugs and compression leaks).
• Inspect Old Plugs: As you remove each old plug, inspect its condition. This can provide valuable insights into your engine's health (e.g., oil fouling, carbon buildup, signs of pre-ignition).

Known issues

Thankfully, the 6.0L L96 V8 engine in the 2019 GMC Sierra 2500HD does not have widely reported common issues specific to spark plug breakage or design flaws, unlike some other engines (e.g., the two-piece spark plugs in certain Ford 3-valve engines which were prone to breaking during removal). The ignition system is robust, and as long as the correct ACDelco or equivalent iridium plugs are used and replaced at the recommended intervals with proper torque, you should experience reliable performance.

Need plugs replaced? Find a shop on Repairius.