2025 Ford F-350 Super Duty Spark Plug Guide

Quick Reference

Why the Right Plug Matters

Choosing the correct spark plug for your 2025 Ford F-350 Super Duty is crucial for optimal engine performance, fuel efficiency, and longevity. The "right" plug isn't just about fitment; it's about heat range, electrode material, and proper gapping.

• Heat Range: Spark plugs are designed with specific heat ranges, dictating how quickly they dissipate heat from the combustion chamber. A "hotter" plug retains more heat, while a "colder" plug dissipates it faster. Using the wrong heat range can lead to pre-ignition (too hot) or fouling (too cold). Ford engineers have meticulously selected the correct heat range for the 6.8L and 7.3L V8 engines, so sticking to OEM or recommended aftermarket plugs is essential.

• Electrode Metal (Iridium vs. Platinum vs. Copper):

  • Iridium: Most modern engines, including the 2025 F-350 gasoline engines, utilize iridium-tipped spark plugs. Iridium is incredibly hard and has a high melting point, allowing for very fine electrodes. This results in a more concentrated spark, better ignition, and significantly extended service intervals (typically 100,000 miles or more).
  • Platinum: Platinum plugs also offer extended life compared to copper, though generally not as long as iridium. They are often found in older vehicles designed for longer-lasting spark plugs. They provide good performance but are typically being phased out in favor of iridium for new applications.
  • Copper: Copper plugs have a large copper core for excellent conductivity, but their electrodes are softer, leading to faster wear. They require more frequent replacement and are generally not specified for modern, long-interval engines like those in the F-350. They are prized in some high-performance or forced-induction engines for their superior spark delivery, but their durability is a trade-off.

How to Gap a Spark Plug

While many modern iridium spark plugs come pre-gapped from the factory, it's always a good practice to verify the gap before installation, especially with aftermarket plugs. Even a small bump during shipping can alter the gap.

1. Obtain a Gap Tool: Use a wire-style or coin-style spark plug gap tool. Avoid using flat feeler gauges as they can damage the fine iridium electrode tip.
2. Check the Gap: Carefully slide the appropriate wire gauge (for wire gap tools) or the edge of the coin tool through the gap between the center and ground electrodes. There should be a slight drag.
3. Adjust if Necessary:
   • To Widen the Gap: Gently pry the ground electrode away from the center electrode using the gap tool's adjustment feature (if available) or by carefully leveraging it against a non-conductive surface.
   • To Narrow the Gap: Gently tap the ground electrode on a clean, hard surface. Be extremely careful not to touch or damage the fragile iridium tip. Make very small adjustments and recheck frequently.

For the 2025 Ford F-350 6.8L and 7.3L engines, the specified gap is 0.051 inches (1.3 mm).

Replacement Procedure Tips

Changing spark plugs on your 2025 F-350's 6.8L or 7.3L V8 will involve working with a coil-on-plug (COP) ignition system. Here are some key tips:

• Coil-on-Plug (COP) Removal: Each spark plug has its own ignition coil mounted directly on top. To access the plugs, you'll need to carefully disconnect the electrical connector from each coil and then remove the bolt or bolts securing the coil. Gently twist and pull the coil straight up to remove it. Avoid yanking or prying that could damage the coil or its boot.
• Anti-Seize Debate: There is ongoing debate about using anti-seize on spark plug threads. Most modern spark plugs, especially those from Motorcraft, NGK, and Denso, have a special coating on the threads that prevents seizing. Applying additional anti-seize can act as a lubricant, leading to over-torquing and potential damage to the cylinder head threads. Ford generally advises against anti-seize for their factory-spec plugs. Always follow the plug manufacturer's recommendations. If you do use anti-seize, reduce the torque value by approximately 10-20% as per manufacturer guidelines to compensate for the lubrication.
• Dielectric Grease on Boots: A small amount of dielectric grease (non-conductive) applied to the inside of the spark plug boot (where it contacts the ceramic insulator of the plug) can help prevent moisture intrusion, inhibit corrosion, and make future removal easier. Apply a thin film, but don't overdo it.
• Torque Wrench is Your Friend: Always use a calibrated torque wrench for spark plug installation. Over-torquing can damage the spark plug, threads in the cylinder head, or lead to plug breakage. Under-torquing can cause the plug to loosen, leading to misfires and potential damage from hot combustion gases escaping.

Known Issues

Fortunately, both the 6.8L and 7.3L "Godzilla" V8 engines in the 2025 Ford F-350 Super Duty are not known for the problematic two-piece spark plug design that plagued some older Ford 3-valve engines (like the 5.4L Triton). This means you generally won't have to worry about broken plug shells during removal. These engines utilize a more conventional, robust one-piece plug design.

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