2021 International MV Spark Plug Type, Gap & Torque Specs

The 2021 International MV is a premier medium-duty workhorse. While the vast majority of these trucks are outfitted with the legendary Cummins B6.7 or L9 diesel engines (which use compression ignition and do not have spark plugs), International also offers this chassis with the PSI 8.8L V8 gasoline and propane (LPG) engines for fleets wanting to avoid diesel emissions equipment. If you are servicing a gas or LPG-powered 2021 International MV, proper spark plug maintenance is critical to keeping this massive 8.8-liter engine pulling heavy loads efficiently.

Quick reference

Note: Cummins B6.7 and L9 diesel engines do not use spark plugs. The following specifications apply exclusively to the PSI 8.8L V8 gasoline/LPG engines.

Why the right plug matters

In a commercial medium-duty application like the International MV, engine load is consistently high. The heat range of the spark plug is crucial. If a plug is too hot, it will cause pre-ignition and potentially catastrophic engine knock under heavy load. If it is too cold, it will foul out during extended idling periods (a common occurrence for bucket trucks or delivery vehicles).

Electrode metal also plays a huge role. Heavy-duty gasoline and LPG engines should exclusively use iridium or double-platinum spark plugs. Standard copper plugs simply cannot withstand the extreme cylinder temperatures and sustained RPMs of a medium-duty truck moving 25,000+ pounds. Iridium provides the durability needed to keep fleet maintenance intervals reasonable.

How to gap a spark plug

Even if your premium iridium spark plugs come "pre-gapped" out of the box, they must be checked before installation. Shipping and handling can easily bump the ground electrode and close the gap.

1. Use the right tool: For precious metals like iridium, avoid using cheap coin-style gauges that can scrape the delicate center electrode. Use a wire-type gap gauge.
2. Check the gap: Slide the correct wire (0.040" for gas, 0.035" for LPG) between the center and ground electrode. It should have a slight "drag" but pass through.
3. Adjust carefully: If the gap needs adjustment, use the bending tool on the gauge to gently pry the ground strap up (to widen) or tap it on a soft wooden workbench (to narrow). Never press directly against the iridium center tip.

Replacement procedure tips

Working on a massive medium-duty truck chassis offers plenty of space, but the sheer size of the 8.8L engine requires a methodical approach.

• Coil-on-Plug (COP) System: The PSI 8.8L utilizes individual coil packs for each cylinder. Take care when unbolting the coils. Blow compressed air into the spark plug wells before removing the old plugs to prevent accumulated dirt and grit from falling directly into the combustion chamber.
• The Anti-Seize Debate: Most modern NGK and ACDelco spark plugs feature a trivalent metal plating that acts as a release agent. Do not use liquid anti-seize on these threads, as it acts as a lubricant and can easily cause you to over-torque the plugs, risking stripped threads in the aluminum cylinder heads.
• Dielectric Grease: Always apply a small, pea-sized amount of dielectric grease inside the tip of the coil boot. This prevents the rubber from fusing to the ceramic insulator over time and helps lock out moisture.

Known issues

While the 8.8L V8 is a robust industrial engine, commercial operating conditions can lead to accelerated wear.

• Accelerated Wear on LPG: Propane (LPG) burns much hotter and drier than gasoline. Fleet managers often find that spark plug gaps widen faster on the LPG models, leading to misfires under load. It is highly recommended to check plugs on LPG engines every 30,000 miles to prevent coil pack strain.
• Boot Degradation: The massive heat generated by the 8.8L engine under continuous load can bake the coil boots. If you are changing the spark plugs, inspect the rubber boots for micro-cracks or white carbon tracks. Replace any brittle boots immediately to prevent spark blowout.

Need plugs replaced? Find a shop on Repairius.