2020 Isuzu NPR Spark Plug Type, Gap & Torque Specs

As an ASE-certified master technician, I know that keeping your commercial fleet running smoothly is critical to your bottom line. If you are operating a gas-powered 2020 Isuzu NPR, you are dealing with a heavy-duty chassis powered by a highly reliable General Motors-sourced 6.0L L96 V8 engine. (Note: The diesel Isuzu NPRs do not use spark plugs). Maintaining the ignition system on this 6.0L V8 is straightforward but requires precise specifications to ensure optimal fuel efficiency and power under heavy loads.

Here is your comprehensive guide to the spark plug type, gap, torque, and replacement procedures for the 2020 Isuzu NPR.

Quick reference

*ACDelco 41-162 supersedes the older 41-110 part number for this GM engine application.

Why the right plug matters

Commercial trucks endure high operating temperatures, extended idling, and heavy payload stresses. Using the correct spark plug is non-negotiable. The heat range of a spark plug dictates how quickly it dissipates heat from the firing tip into the cylinder head. An incorrect heat range can lead to carbon fouling (if too cold) or pre-ignition and engine damage (if too hot).

Electrode material is just as vital. The OEM specification for this engine is Iridium. Iridium is significantly harder and more durable than platinum or traditional copper. While copper plugs offer excellent conductivity, they wear out rapidly and would require replacement every 15,000 miles—unacceptable for fleet maintenance. Platinum offers a middle ground, but Iridium allows the 2020 Isuzu NPR to confidently reach a 100,000-mile service interval without sacrificing spark strength or efficiency.

How to gap a spark plug

Even though modern Iridium spark plugs come pre-gapped from the factory, an ASE-certified technician always verifies the gap before installation. Plugs can be dropped or mishandled during shipping.

To check the gap on your 2020 Isuzu NPR's plugs:

1. Use a wire-style or feeler gauge tool rather than a cheap coin-style gauge.
2. Gently slide the 0.040 in (1.01 mm) gauge between the center and ground electrode. It should pass through with a slight "drag."
3. Important: Iridium center electrodes are incredibly brittle. Never pry against the center electrode!
4. If you need to widen the gap, use a specialized gapping tool to apply a light bend to the ground strap only. If it's too wide, gently tap the ground strap on a hard surface to close it, then re-measure.

Replacement procedure tips

The 6.0L GM V8 in the Isuzu NPR uses a coil-near-plug setup. Each cylinder has its own individual ignition coil mounted to the valve cover, connected to the spark plug via a short, high-tension wire.

• Removing the wires: Over time, the rubber boots of the spark plug wires can bake onto the spark plug ceramic due to exhaust manifold heat. Twist the boot side-to-side to break the seal before pulling. Pulling directly on the wire will likely rip the terminal right out of the boot. Pro tip: Plan to replace the plug wires concurrently with the spark plugs.
• The anti-seize debate: Most modern premium spark plugs (including NGK and ACDelco) feature a trivalent metal plating on the threads, acting as a built-in anti-seize. Do not add traditional liquid anti-seize to these threads. Adding anti-seize acts as a lubricant and will cause you to accidentally over-torque the plugs, risking severe cylinder head thread damage. Stick to the dry torque spec of 11 lb-ft.
• Dielectric grease: 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, inhibits voltage leaks, and makes future removal much easier.

Known issues

Unlike the notorious older Ford 3-valve engines that suffered from broken 2-piece spark plug shells wedged in the cylinder head, the GM 6.0L V8 in your Isuzu NPR is generally free of catastrophic plug defects.

However, a known issue with this specific fleet configuration is heat stress on the spark plug wires. Because of the commercial vehicle's tight engine bay and poor airflow around the exhaust manifolds, the short ignition wire boots are highly susceptible to cracking and baking onto the plugs. If your NPR experiences a misfire under heavy load or going uphill, check for tracking marks or cracked porcelain caused by degraded spark plug wire boots arcing to the engine block.

Need plugs replaced? Find a shop on Repairius.