2023 GMC Yukon — Spark Plug Type & Gap

As an ASE-certified master technician, I can tell you that keeping up with spark plug maintenance on modern GM V8 engines is critical for preserving performance, fuel economy, and emissions compliance. The 2023 GMC Yukon relies on advanced direct-injected 5.3L and 6.2L V8 engines (note: the 3.0L Duramax diesel option does not use spark plugs). To keep these engines firing perfectly, installing the correct spark plugs with the precise gap and torque is essential.

Quick reference

Note: The 3.0L Duramax inline-6 turbo-diesel is a compression-ignition engine and does not utilize spark plugs.

Why the right plug matters

Choosing the correct spark plug is more than just making sure the threads fit. The heat range of the plug dictates how efficiently it can pull heat away from the firing tip into the cylinder head. An incorrect heat range can lead to pre-ignition (too hot) or carbon fouling (too cold).

Additionally, electrode metal plays a massive role in modern engines. Copper plugs offer great conductivity but wear out rapidly. Platinum provides a good balance, but for high-compression, direct-injected engines like the 2023 Yukon’s EcoTec3 V8s, Iridium is the standard. Iridium is significantly harder and more durable than platinum, allowing for a finer wire electrode that concentrates the electrical spark, offering more efficient combustion and a 100,000-mile service life.

How to gap a spark plug

Even if your ACDelco or NGK plugs come "pre-gapped," shipping and handling can sometimes alter that gap. It is best practice to verify them before installation.

1. Use the right tool: A wire-type feeler gauge is highly recommended over a coin-style gauge, especially for iridium plugs, to avoid scraping the fragile precious metal coating off the center electrode.
2. Measure: Gently slide the 0.040" (1.0 mm) wire gauge between the center and ground electrode. It should pass through with a slight "drag."
3. Adjust (if necessary): If the gap is too tight, use the bending tool on your gauge to lightly bend the ground strap up. If it’s too loose, gently tap the ground strap against a soft wooden workbench. Never pry directly against the iridium center tip.

Replacement procedure tips

Replacing plugs on the 2023 GMC Yukon’s 5.3L or 6.2L V8 is a relatively straightforward process, but requires attention to detail.

• Coil-on-Plug Removal: The Yukon uses an individual coil for each cylinder with a short plug wire boot. Gently twist the boot before pulling to break the heat seal. Do not yank on the wire itself, or you may damage the internal conductor.
• The Anti-Seize Debate: GM typically advises against using anti-seize compound on new spark plug threads. Most modern ACDelco and NGK plugs feature a trivalent metal plating that acts as a release agent. Adding anti-seize acts as a lubricant, which can easily cause you to over-torque the plug and damage the aluminum cylinder head threads.
• Dielectric Grease: Always apply a small dab of dielectric grease to the inside of the spark plug boot before reinstallation. This prevents moisture intrusion, stops high-voltage tracking, and ensures the boot won't stick to the plug during the next service.

Known issues

While the dreaded broken 2-piece spark plug shell issue was famous on the older Ford 3-valve V8s, GM's EcoTec3 engines have their own quirks.

Modern GM ignition coils are highly sensitive, and some utilize ionization-sensing technology to monitor combustion quality and knock. Installing cheap, counterfeit, or incorrect aftermarket copper plugs can disrupt this feedback loop, leading to phantom misfire codes (P0300), reduced power, and poor transmission shifting.

Additionally, take care when removing the plugs from the rear cylinders (especially cylinders 7 and 8 near the firewall). It is easy to accidentally bind your socket against the steering shaft or firewall, which can crack the porcelain insulator of the new plug upon installation, causing an immediate misfire. Always use a proper spark plug socket with a rubber insert or magnetic hold, combined with a universal swivel joint.

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