2018 Ford F-350 Super Duty: Spark Plug Type, Gap & Torque

Quick Reference

Why the right plug matters

Choosing the correct spark plug for your 2018 F-350 is more than just a matter of fitment. The spark plug is a critical component in the combustion process, and its design directly impacts engine performance, fuel economy, and longevity. Key factors to consider are the heat range and the electrode material.

• Heat Range: This refers to the spark plug's ability to dissipate heat. A plug that is too "hot" can lead to pre-ignition, while a "cold" plug can foul more easily. For the 6.2L V8 and 6.8L V10 engines in the 2018 F-350, a plug within the specified heat range is essential for optimal combustion.

• Electrode Material: The material of the center and ground electrodes determines the plug's lifespan and performance characteristics.

  • Iridium: As specified for the OEM plugs in the F-350, iridium is a precious metal with an extremely high melting point. This allows for a very fine-wire center electrode, which improves ignitability and reduces the voltage required to create a spark. Iridium plugs offer the longest service life, typically around 100,000 miles.
  • Platinum: Another long-life option, platinum plugs offer excellent performance and durability, though not quite to the level of iridium.
  • Copper: While once the standard, copper plugs have a much shorter lifespan (typically 20,000-30,000 miles) and are not recommended for the 2018 F-350.

How to gap a spark plug

Properly gapping your spark plugs is crucial for a strong, consistent spark. The gap is the distance between the center and ground electrodes. Even pre-gapped plugs should be checked before installation.

1. Use a feeler gauge or a spark plug gap tool. These tools have wires or blades of precise thicknesses.
2. Gently slide the correct thickness gauge between the electrodes. For the 2018 F-350, you'll be aiming for a gap between 0.041 and 0.047 inches.
3. If the gap is too wide, gently tap the ground electrode on a hard surface to close the gap slightly.
4. If the gap is too narrow, use the hook on your gap tool to carefully bend the ground electrode open.

Replacement procedure tips

The 2018 F-350 utilizes a coil-on-plug (COP) ignition system, which means each spark plug has its own ignition coil mounted directly on top of it. This design eliminates the need for a distributor and spark plug wires, but it does require a few extra steps during plug replacement.

• Coil-on-Plug Removal: To access the spark plugs, you must first remove the ignition coils. This is typically done by disconnecting the electrical connector and removing a single bolt holding the coil in place. Gently twist and pull the coil straight up to remove it from the spark plug.

• The Anti-Seize Debate: There is some debate in the automotive community about the use of anti-seize on spark plug threads. The concern is that the anti-seize can act as a lubricant, leading to over-torquing of the plugs. However, many technicians still recommend a small amount of anti-seize on the threads to prevent them from seizing in the cylinder head, especially in engines with aluminum heads like those in the F-350.

• Dielectric Grease: It is highly recommended to apply a small amount of dielectric grease to the inside of the spark plug boot before reinstalling the ignition coil. This helps to prevent voltage leaks and makes it easier to remove the coil in the future.

Known issues

While the 2018 F-350 does not suffer from the infamous two-piece spark plug breakage issue that plagued earlier Ford 3-valve engines, it's still important to be aware of potential problems. Cracked porcelain insulators can occur on any spark plug, and if a piece of the insulator falls into the cylinder, it can cause serious engine damage. Always inspect new spark plugs for cracks before installation.

Need plugs replaced? Find a shop on Repairius.