2022 Chevrolet Silverado 2500HD — Spark Plug Type, Gap & Torque

Quick reference

Note: GM prints the official spark plug part number and gap on the under-hood emissions label. Always verify by VIN to avoid mid-year supersessions.

Why the right plug matters

The 2022 Silverado 2500HD’s 6.6L L8T gas V8 is engineered for heavy loads, long idle time, and wide temperature swings. Using the correct spark plug ensures the plug’s heat range matches the cylinder head’s thermal characteristics so the plug can shed heat properly. A plug that’s too hot can cause pre-ignition and detonation; too cold and it can foul.

Electrode material is equally important. Iridium fine-wire plugs are the OE choice for the L8T because they fire reliably with less required voltage and resist gap erosion, supporting long service intervals around 100,000 miles. Platinum plugs offer good life but typically shorter than iridium. Conventional copper/nickel plugs have strong initial performance but erode quickly, making them a poor fit for modern ignition systems and extended intervals.

Stick with resistor-type, projected-tip plugs of the exact design GM specifies. Avoid changing heat range unless you’re following a GM calibration with specific guidance (for example, severe-duty calibration). For the Duramax L5P diesel, ignition is by compression—no spark plugs are used.

How to gap a spark plug

Most iridium plugs come pre-gapped. Still, confirm the gap against the under-hood label or service information.

• Identify the correct spec (commonly about 0.044 in / 1.12 mm for the L8T, but verify).
• Use a wire-style gap gauge. Avoid coin/disc tools that can stress the fine center electrode.
• Check drag at multiple points around the ground strap. The gauge should pass with a light, even drag.
• If adjustment is needed, support the ground strap and bend it slightly at the base. Do not pry on or touch the iridium center tip.
• Re-check the gap after adjustment.

Replacement procedure tips (6.6L L8T gas)

The L8T uses individual ignition coils mounted to the valve covers with short coil-to-plug boots (coil-near-plug). There is no distributor.

• Battery and access: Disconnect the negative battery cable. Remove the engine cover. For better access to rear cylinders, a short wobble extension and a 5/8 in (16 mm) spark plug socket help. You may loosen the intake duct or move small brackets/lines for clearance as needed.
• Keep debris out: Blow out the plug wells with compressed air before removing plugs.
• Remove boots: Unclip the coil harness connectors if you need coil movement. Twist the plug boots to break them free, then pull straight off the plugs. Inspect for oil or coolant intrusion.
• Remove plugs: Work on a cool aluminum head. Break loose, then spin out by hand. If resistance is high, work the plug out gently; do not force it.
• Install new plugs: Confirm part number and gap. Start threads by hand at least two full turns to avoid cross-threading the aluminum head. Torque to 15 lb-ft (20 Nm) unless GM service info for your VIN states otherwise.
• Anti-seize: GM/ACDelco advise no anti-seize on plated OE plugs. If you choose to use it against guidance, reduce torque by ~20–30% to avoid over-tightening.
• Boots and grease: Apply a thin film of dielectric grease inside each boot to prevent moisture intrusion and ease future service. Re-seat boots until you feel a positive engagement. Reconnect coil connectors and reinstall any removed components.

Known issues and notes

• Diesel vs gas: The L5P Duramax diesel uses glow plugs and compression ignition—no spark plugs. Do not order spark plugs for diesel trucks.
• Two-piece plug breakage: The notorious Ford 3-valve V8 two-piece plug issue does not apply here. GM L8T plugs are a one-piece design.
• Over-torque/cross-threading: The L8T aluminum heads use tapered-seat plugs. Over-torque or dry cross-threading can damage threads. Always hand-start and use a torque wrench.
• Water intrusion and carbon tracking: Deep water crossings or aggressive engine bay washing can allow moisture into plug boots, leading to carbon tracking and misfires. Replace affected boots and plugs; add dielectric grease during reassembly.
• Misfire under load: Often traced to an enlarged gap on high-mileage plugs. Inspect gap and replace on schedule.

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