2025 GMC Yukon Spark Plug Type, Gap & Torque Specs

As an ASE-certified master technician, I’ve seen firsthand how crucial the ignition system is on modern, high-compression direct-injected engines. If you are servicing a 2025 GMC Yukon, you are dealing with General Motors' advanced Gen V V8 engines (the 5.3L L84 or the 6.2L L87). These engines demand specific spark plug requirements to maintain peak efficiency, prevent misfires, and protect the catalytic converters.

(Note: The 2025 Yukon is also offered with a 3.0L Duramax inline-six. Being a diesel engine, it utilizes glow plugs rather than spark plugs, so it is excluded from this guide.)

Here is the essential data you need before you crack open the hood.

Quick reference

Why the right plug matters

Modern GM V8s are incredibly sensitive to spark plug specifications. The factory ACDelco plugs are Double Iridium. Why iridium? Iridium is significantly harder and more durable than platinum or traditional copper. The fine-wire iridium center electrode requires less voltage to fire while providing a highly concentrated spark, which is absolutely mandatory for igniting the lean, high-pressure fuel mixtures in these direct-injected engines.

Furthermore, heat range is paramount. Putting a "hotter" plug in an engine designed for a cooler plug can lead to pre-ignition and catastrophic piston damage. Sticking with the OEM ACDelco iridiums or equivalent NGK/Denso replacements ensures you maintain the precise heat range engineered for your Yukon's combustion chambers.

How to gap a spark plug

Even though most premium iridium spark plugs come pre-gapped from the factory, an ASE best practice is to always verify the gap before installation. Shipping drops can easily close a gap.

1. Use the right tool: Do not use a cheap coin-style gauge on iridium plugs. The center electrode is fragile. Use a wire-style feeler gauge.
2. Check the gap: Gently slide the 0.038" or 0.040" wire between the center and ground electrode. It should have a slight "drag" without forcing it.
3. Adjust carefully: If the gap is too tight, use the adjustment tool on the gauge to gently bend the ground strap outward. Never pry against the delicate iridium center tip—you will snap it.

Replacement procedure tips

The 2025 Yukon utilizes a coil-on-plug (COP) ignition architecture, though it technically uses short spark plug wires connecting the coil packs to the plugs.

• The Anti-Seize Debate: GM officially recommends against using anti-seize on modern spark plug threads. The factory ACDelco and premium NGK plugs feature a trivalent metal plating that acts as a release agent. Adding liquid anti-seize alters the torque coefficient, usually resulting in over-torquing, which can crack the porcelain insulator or damage the aluminum cylinder head threads. Install them dry.
• Boot Maintenance: Always apply a small dab of dielectric grease to the inside of the spark plug wire boot before snapping it onto the new plug. This prevents moisture intrusion, halts voltage leaks, and ensures the boot won't fuse to the ceramic insulator over the next 100,000 miles.
• Tooling: You will need a 5/8-inch spark plug socket, preferably a magnetic swivel socket, and various extensions to navigate the engine bay.

Known issues

While the 2025 Gen V V8s don't suffer from the notorious broken two-piece plug issues seen in older Ford 3-valve engines, they present their own quirks:

• Tight clearances: Accessing the rear cylinders (particularly cylinder 8 on the passenger side near the firewall) can be frustrating. You may need to unbolt the dipstick tube bracket or remove the coil pack bracket entirely to gain straight access. Do not attempt to install the plug at an angle, as cross-threading an aluminum head is an expensive mistake.
• Coil sensitivity: GM's engine management relies heavily on the specific electrical resistance of the ignition system to monitor combustion quality and detect misfires. Using cheap copper plugs or counterfeit online plugs with incorrect resistance values can confuse the ECM, causing phantom misfire codes and rough idling. Stick to genuine parts.

Need plugs replaced? Find a shop on Repairius.