2018 GMC Sierra 2500HD Spark Plug Type & Gap

Quick reference

Why the right plug matters

Spark plugs are vital for your engine's performance, fuel economy, and emissions. Using the correct spark plug for your 2018 GMC Sierra 2500HD is crucial. The 6.0L LY6 VORTEC V8 engine in your Sierra is designed to run with specific spark plugs, primarily iridium-tipped, from the factory.

Heat Range: Spark plugs are engineered with a specific "heat range," which refers to their ability to dissipate heat from the combustion chamber. A "hotter" plug retains more heat, while a "cooler" plug dissipates more. Using a plug with an incorrect heat range can lead to pre-ignition (too hot) or fouling (too cold), both of which can cause damage or poor engine performance.

Electrode Metal:

• Iridium: The standard for modern engines like your 2018 Sierra, iridium plugs offer exceptional durability and a long lifespan due to iridium's extremely high melting point and strength. They typically last 100,000 miles or more and provide consistent, strong sparks.
• Platinum: Another long-lasting option, platinum plugs offer good durability but generally don't match iridium's lifespan. They are often found in older vehicles designed for extended service intervals.
• Copper: While copper is an excellent conductor, copper-tipped plugs have a much shorter lifespan due to copper's lower melting point and softness. They are rarely used in modern vehicles requiring long service intervals and are generally found in older, performance-oriented applications or very basic engines where frequent replacement is acceptable.

How to gap a spark plug

Your 2018 GMC Sierra 2500HD's 6.0L LY6 engine uses iridium plugs which come pre-gapped from the factory. It is generally not recommended to gap iridium spark plugs. The fine wire iridium electrode can be easily damaged if you attempt to adjust the gap with traditional gapping tools. If a plug's gap is incorrect out of the box, it's best to replace the plug rather than attempting to adjust it.

However, for other plug types, or if you absolutely must check the gap of an iridium plug with extreme caution:

1. Use a wire gauge tool: A wire-type spark plug gapping tool is preferred over a ramp-style tool, as it is less likely to damage the delicate electrode.
2. Check the gap: Slide the correct size wire through the gap between the central electrode and the ground strap. It should be a snug fit.
3. Adjust (if necessary and with extreme care): If the gap is too small, use the gapping tool to gently bend the ground electrode outwards. If the gap is too large, gently tap the ground electrode on a hard surface to close the gap. Again, this is strongly discouraged for iridium plugs.

Replacement procedure tips

Replacing spark plugs on your 2018 GMC Sierra 2500HD's 6.0L LY6 VORTEC V8 is a relatively straightforward job for a DIY mechanic with the right tools.

1. Safety First: Ensure the engine is cool. Disconnect the negative battery terminal before starting any work.
2. Access: The spark plugs are located under the ignition coils (coil-on-plug system). You will need to remove the engine cover and potentially some air intake components to gain adequate access.
3. Coil-on-Plug Removal: Disconnect the electrical connector from each ignition coil. Then, unbolt the coil (typically one or two bolts) and gently twist and pull upwards to remove it from the spark plug. Be careful not to pull on the wire harness.
4. Cleaning: Before removing the old spark plug, use compressed air to blow any dirt or debris away from the spark plug well. This prevents contaminants from falling into the combustion chamber once the plug is removed.
5. Spark Plug Removal: Use a spark plug socket (a deep socket with a rubber insert to protect the porcelain and hold the plug) and a ratchet to loosen and remove the old plugs. Turn counter-clockwise.
6. Anti-Seize Debate: The 6.0L LY6 engine utilizes aluminum cylinder heads. Some manufacturers, including ACDelco, specify that anti-seize should not be used on spark plug threads with factory-coated spark plugs, as it can alter the torque readings and potentially lead to over-tightening or issues with the plug