2021 Jeep Grand Cherokee Spark Plug Specs & Replacement Guide

As an ASE-certified master technician, I’ve replaced countless sets of spark plugs in Mopar vehicles. The 2021 Jeep Grand Cherokee (WK2 generation) features some robust engine options, from the ubiquitous 3.6L Pentastar V6 to the legendary 5.7L Hemi V8. Maintaining the ignition system on these engines is critical for fuel economy, emissions, and smooth power delivery.

Below is your complete guide to spark plug types, gaps, torque specifications, and replacement intervals for the 2021 Jeep Grand Cherokee.

Quick reference

*Note: Hemi V8 engines feature a dual-spark system requiring two spark plugs per cylinder (16 plugs total).

Why the right plug matters

Modern engines are incredibly sensitive to spark plug specifications, primarily regarding heat range and electrode metal.

• Heat Range: The heat range determines how fast the plug dissipates heat from the firing tip into the cylinder head. Installing a plug with a heat range that is too hot can lead to pre-ignition and catastrophic engine damage, while a plug that is too cold will foul out with carbon deposits.
• Electrode Metal: The 2021 Grand Cherokee engines are designed exclusively for Iridium spark plugs. Iridium is significantly harder and more durable than platinum or standard copper, allowing the center electrode to be wire-fine. This concentrates the spark for better combustion efficiency and allows the plugs to easily survive the 100,000-mile service interval. Never downgrade a factory-iridium vehicle to copper or platinum plugs.

How to gap a spark plug

Even though most premium iridium spark plugs come pre-gapped from the factory, you should always verify the gap before installation. Dropped boxes in transit can easily close a gap.

1. Use the right tool: Use a wire-type gauge or a proper feeler gauge. Coin-style gauges can easily snap the brittle iridium tip of the center electrode.
2. Measure: Gently pass the 0.043" wire through the gap. It should slide through with a slight drag.
3. Adjust: If the gap is too tight, use the bending tool on your gauge to slightly pull the ground strap away. If it’s too loose, gently tap the back of the ground strap on a hard, clean surface. Never pry against the center iridium electrode—it will break, ruining the plug.

Replacement procedure tips

Replacing plugs on the 2021 Grand Cherokee involves a coil-on-plug (COP) ignition system, meaning there are no spark plug wires or distributors.

• 3.6L V6 Pentastar Intake Removal: To access the driver-side bank (cylinders 2, 4, 6) on the 3.6L, you must remove the upper intake manifold (plenum). It sounds intimidating, but it only takes about 15–20 minutes for an experienced tech. Always replace the upper intake manifold gaskets while you are in there to prevent vacuum leaks.
• 5.7L/6.4L Hemi Dual Plugs: Remember that you are buying and installing 16 spark plugs. Take your time, as the rear plugs near the firewall require swivels and extensions to access properly.
• The Anti-Seize Debate: Mopar and NGK strongly advise against using anti-seize on the spark plug threads. The OEM plugs feature a special trivalent metal plating that acts as a release agent. Adding anti-seize acts as a lubricant, which alters your torque reading and can easily cause you to over-torque and strip the aluminum cylinder head threads. Install them dry.
• Dielectric Grease: Apply a small dab of dielectric grease to the inside of the ignition coil boot. This prevents the rubber from fusing to the ribbed ceramic insulator of the spark plug, making the next tune-up much easier, while also sealing out moisture.

Known issues

• 3.6L Spark Plug Tube Seals: When pulling the ignition coils out of the 3.6L V6, inspect the rubber boots. If they are dripping with engine oil, your valve cover spark plug tube seals have failed. You will need to replace the valve cover gaskets and tube seals to prevent the oil from causing engine misfires.
• Ignition Coil Lifespan: While you don't necessarily have to replace coils at 100k miles, Mopar ignition coils exposed to extreme heat (especially on the 5.7L/6.4L models) can begin to weaken by this mileage. If your vehicle has high mileage and a slight idle stumble even after new plugs, worn coils are the likely culprit.

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