2018 Jeep Grand Cherokee Spark Plug Specs & Replacement Guide

As an ASE-certified master technician, I’ve serviced countless Jeep Grand Cherokees. The 2018 model year spans a wide range of engine options—from the reliable 3.6L Pentastar V6 to the monstrous 6.2L Supercharged Trackhawk. Getting the spark plug specifications right is critical to maintaining the performance, fuel economy, and emission standards of your Jeep.

Below is your comprehensive guide to the spark plug part numbers, gaps, torque specs, and replacement intervals for the 2018 Jeep Grand Cherokee.

Quick reference

*Note: All V8 Hemi engines (5.7L, 6.4L, and 6.2L) require two spark plugs per cylinder (16 plugs total).

Why the right plug matters

Modern engines are incredibly sensitive to the type of spark plug used. The 2018 Grand Cherokee engines require specific heat ranges to prevent pre-ignition (pinging) or plug fouling.

Electrode metal plays a massive role in replacement intervals and performance:

• Iridium and Platinum: The Pentastar V6 and Hemi V8s use iridium or platinum-tipped plugs from the factory. These metals are incredibly dense and resist spark erosion, which is why they boast a 100,000-mile interval.
• Copper: While copper is an excellent conductor, standard copper core plugs will wear out in as little as 30,000 miles. Stick to the OEM-specified Iridium or Double-Platinum plugs to avoid having to tear the intake manifold off your 3.6L prematurely.

How to gap a spark plug

Most modern iridium spark plugs come pre-gapped, but a master tech always verifies the gap before installation, as plugs can be dropped during shipping.

1. Use the right tool: Do not use a cheap coin-style gauge on iridium plugs; the brittle iridium center electrode can easily snap. Use a wire-style gap gauge or a specialized feeler gauge.
2. Check the gap: Slide the correct wire gauge between the center and ground electrode. It should pass through with a slight "drag."
3. Adjust safely: If the gap is too tight, use the bending tool on your gauge to lightly bend the ground electrode outward. Never pry against the center electrode!

Replacement procedure tips

Replacing plugs on a 2018 Grand Cherokee varies wildly depending on your engine. All 2018 gas engines use a Coil-On-Plug (COP) ignition system.

• 3.6L Pentastar V6: You must remove the upper intake manifold (plenum) to access the driver's side bank of spark plugs. Make sure to buy a new set of upper intake manifold gaskets beforehand. Torquing the manifold bolts properly upon reassembly is critical to avoid vacuum leaks.
• Hemi V8s (5.7L, 6.4L, 6.2L): You will be replacing 16 spark plugs! Access to the rear cylinders (especially near the firewall) is tight. You will need a variety of extensions and swivel sockets.
• The Anti-Seize Debate: NGK explicitly states not to use anti-seize on their zinc-plated plugs, as it acts as a lubricant and can easily lead to over-torquing the plug and damaging the aluminum cylinder head. Install them dry.
• Dielectric Grease: Always apply a small dab of dielectric grease to the inside of the ignition coil boot. This prevents the rubber from fusing to the ceramic spark plug shell, making your next tune-up much easier.

Known issues

• Hemi Ignition Coil Boots: On the 5.7L and 6.4L, the rubber coil boots that reach down into the deep spark plug tubes tend to dry rot and crack over time due to high engine bay heat. If you see white arcing marks on the inside of the boot or experience a misfire under load, replace the coil boots along with the plugs.
• Pentastar Spark Plug Tube Seals: When pulling the coils out of the 3.6L, check for engine oil pooling on top of the spark plugs. This indicates failing spark plug tube seals in the valve cover, which will eventually cause misfires.

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