2017 GMC Sierra 2500HD Spark Plug Spec Guide: Type, Gap & Torque

When it comes to maintaining the relentless pulling power of your 2017 GMC Sierra 2500HD, proper ignition system maintenance is non-negotiable. As an ASE-certified master technician, I can tell you firsthand that slapping just any spark plug into this heavy-duty rig is a recipe for misfires, poor fuel economy, and potential catalytic converter damage.

While the legendary 6.6L Duramax diesel variant of this truck utilizes glow plugs instead of spark plugs, the stout 6.0L V8 gas engine (L96/LC8) relies on a precision-engineered coil-on-plug ignition system. Here is the ultimate guide to the spark plug specifications, gaps, and torque limits for your 2017 GMC Sierra 2500HD.

Quick reference

(Note: The 6.6L Duramax is a diesel engine and does not use spark plugs.)

Why the right plug matters

Choosing the correct spark plug involves far more than simply finding threads that fit. The 6.0L Vortec engine requires a specific heat range to effectively transfer heat away from the firing tip into the cylinder head. If the plug runs too hot, you risk pre-ignition and engine pinging under heavy towing loads. If it runs too cold, the plug will foul with carbon deposits.

Electrode material is equally critical. For the 2017 Sierra 2500HD, iridium is mandatory. Copper plugs wear out too fast, and standard platinum plugs can't withstand the intense combustion temperatures of modern high-compression HD truck engines. Iridium is significantly harder and more durable than both, ensuring stable spark performance for nearly 100,000 miles.

How to gap a spark plug

Even if your ACDelco or NGK iridium plugs come "pre-gapped" out of the box, shipping and handling can bump the ground strap out of spec. Always verify the gap.

1. Use the right tool: Do not use a cheap coin-style gauge on iridium plugs. The fragile iridium center tip can easily snap. Use a specialized wire gauge or feeler gauge.
2. Measure gently: Slide the 0.040 in (1.01 mm) wire between the electrodes. There should be a slight drag, but it shouldn't force the electrodes apart.
3. Adjusting the gap: If the gap is too tight, use the bending tool on the gap gauge to gently pry the ground strap outward. Never pry against the center electrode!

Replacement procedure tips

Replacing plugs on the 6.0L V8 is a relatively straightforward coil-on-plug procedure, but it demands attention to detail:

• Access: The passenger side rear plugs can be a bit tight near the firewall, but removing the inner fender liners makes the job incredibly fast and gives you direct line-of-sight to the plugs.
• Coil-on-plug removal: Remove the 10mm bolt holding the coil pack, twist the boot slightly to break the seal, and pull straight out.
• The anti-seize debate: Modern ACDelco and NGK spark plugs feature a special trivalent metal plating that acts as a release agent. Do not use anti-seize on these threads. Adding anti-seize alters the friction coefficient, meaning your torque wrench will over-tighten the plug, potentially stripping the aluminum cylinder head.
• Dielectric grease: Apply a small dab of dielectric grease inside the tip of the new spark plug boot before reinstallation. This prevents moisture intrusion, stops voltage leaks, and ensures you won't tear the boot during the next tune-up.

Known issues

While the 6.0L V8 doesn't suffer from the infamous two-piece spark plug breakage of the older Ford 3-valve engines, it does have its quirks.

The most common headache during a plug change on the 2017 Sierra 2500HD is the spark plug wire heat shields. General Motors uses metal heat shields surrounding the plug boots to protect them from the exhaust manifolds. Over time and thousands of heat cycles, the rubber boots fuse to the ceramic plug shell, and pulling on the metal shield often destroys the wire. Always plan to replace the short spark plug wires along with your spark plugs to avoid misfires from torn boots.

Need plugs replaced? Find a shop on Repairius.