2025 GMC Sierra 1500 Spark Plug Type, Gap & Torque Specs

As an ASE-certified master technician, I’ve seen firsthand how a simple spark plug replacement can restore power and fuel economy to a modern truck. If you are tuning up a 2025 GMC Sierra 1500, it is critical to use the correct OEM or equivalent aftermarket plugs, verify the gap, and torque them properly to ensure peak performance from your engine.

Below is your comprehensive guide to the spark plug specifications, torque ratings, and replacement intervals for the 2025 GMC Sierra 1500 gas engines. (Note: The 3.0L Duramax diesel engine uses glow plugs, not spark plugs, and is excluded from this guide).

Quick reference

Why the right plug matters

Modern engines like GM’s EcoTec3 V8s and the high-boost 2.7L TurboMax are incredibly sensitive to spark plug design. Using the correct heat range is vital. If a plug is too hot, it can cause pre-ignition and catastrophic engine knock; if it’s too cold, carbon fouling will occur, leading to misfires.

Electrode metal is equally important. The 2025 Sierra 1500 requires iridium spark plugs straight from the factory. Iridium is significantly harder and more durable than platinum or traditional copper. While copper conducts electricity well, it degrades rapidly under the intense pressures of a modern combustion chamber. Iridium provides a sharp, concentrated spark that ensures complete combustion, supporting the truck’s Dynamic Fuel Management (DFM) system and extending service intervals up to nearly 100,000 miles on the V8s.

How to gap a spark plug

Even though most premium iridium spark plugs come pre-gapped from the factory, you should always verify the gap before installation. A plug could have been dropped during shipping, closing the gap.

1. Use the right tool: For fine-wire iridium plugs, avoid the old-school "coin-style" gapping tools, as they can easily snap the brittle iridium center electrode. Use a wire-style feeler gauge.
2. Measuring: Gently slide the wire gauge between the center and ground electrode. It should pass through with a slight "drag."
3. Adjusting: If the gap is too tight, use the bending notch on your gapping tool to lightly bend the ground electrode upward. Never pry against the center iridium tip. If it’s too loose, gently tap the ground electrode on a soft wooden workbench to close it slightly.

Replacement procedure tips

The 2025 Sierra utilizes a coil-on-plug (COP) ignition system, meaning each spark plug has its own dedicated ignition coil bolted directly above it (or adjacent to it with a short wire on the V8s).

• Coil removal: Always unclip the wiring harness connectors carefully. Modern plastic heat cycles can make these tabs brittle. Use a gentle rocking motion to pull the coil boot off the plug.
• The Anti-Seize Debate: General Motors explicitly states not to use anti-seize compound on the spark plug threads. ACDelco and NGK plugs feature a special zinc or nickel plating that prevents galvanic corrosion. Adding anti-seize alters the friction coefficient, which often leads to over-torquing and stripping the aluminum cylinder head threads.
• Dielectric Grease: Apply a small pea-sized amount of dielectric grease inside the tip of the coil boot. This prevents moisture intrusion, stops high-voltage tracking, and ensures the boot won't bake onto the ceramic ribbed insulator of the new plug.

Known issues

While the 2025 Sierra doesn't suffer from the infamous multi-piece spark plug breakage seen in older Ford 3-valve engines, GM engines do have their quirks.

On the 5.3L and 6.2L V8s, the ignition coils are highly sensitive to resistance changes. GM uses ionization-sensing technology through the spark plugs to detect knock and misfires. If you install cheap aftermarket copper or platinum plugs, the altered electrical resistance can confuse the ECM, leading to false knock retard readings, sluggish acceleration, and erratic shifting. Stick to the OEM ACDelco or equivalent NGK iridium plugs to keep the engine management system happy. Furthermore, be cautious when removing the plug wires on the V8s; they often seize onto the spark plug and tear during removal, so it is highly recommended to have a spare set of ignition wires on hand before starting the job.

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