2025 Subaru Outback Spark Plug Specs

Quick Reference

Why the Right Plug Matters

Choosing the correct spark plug for your 2025 Subaru Outback is paramount for optimal engine performance, fuel efficiency, and longevity. The spark plug is a seemingly small component, but it plays a critical role in igniting the air-fuel mixture in your engine's cylinders.

Heat Range

Spark plugs are designed with a specific "heat range," which refers to their ability to dissipate heat. A plug that is too hot can lead to pre-ignition and detonation, causing engine damage. A plug that is too cold can lead to fouling, where carbon deposits build up on the electrode, hindering spark delivery. Subaru engineers have carefully selected the ideal heat range for the FB25 and FA24F engines, so always stick to the recommended OEM or equivalent plugs.

Electrode Metal (Iridium vs. Platinum vs. Copper)

Modern Subaru engines, including those in the 2025 Outback, predominantly use iridium spark plugs. Iridium is an incredibly hard and durable metal, allowing for very fine electrodes. This thin electrode design concentrates the electrical field, producing a stronger, more consistent spark. The key advantages of iridium plugs include:

• Longer Service Life: Iridium plugs can last significantly longer than traditional copper or even platinum plugs, which is why Subaru specifies a 60,000-mile replacement interval.
• Improved Ignition: The fine iridium tip provides a more precise and powerful spark, leading to better combustion and reduced misfires.

While platinum plugs offer a longer life than copper, they don't match the longevity or performance of iridium. Copper plugs, while excellent conductors, wear down much faster and are generally not recommended for modern engines designed for iridium.

How to Gap a Spark Plug

Properly gapping a spark plug is crucial for a strong spark and efficient combustion. The gap is the distance between the center electrode and the ground electrode. While many iridium plugs come pre-gapped from the factory, it's always wise to double-check, especially if you're using an aftermarket plug. However, exercise extreme caution when gapping iridium plugs.

1. Use the Correct Tool: Always use a wire-type spark plug gapping tool. Never use a disc-style gapper, as it can damage the delicate iridium tip.
2. Measure and Adjust: Carefully slide the correct thickness wire gauge (0.044 inches or 1.1 mm for the 2.5L, and 0.030 inches or 0.75 mm for the 2.4L Turbo) between the electrodes. If adjustment is needed, gently bend only the ground electrode. Do not pry against the center electrode.
3. Avoid Damage: Iridium tips are brittle. Impacting them or applying excessive force can easily cause damage, rendering the plug useless.

Replacement Procedure Tips (2025 Subaru Outback)

Replacing spark plugs on a Subaru Boxer engine, while doable for a DIYer, requires patience due to the horizontally opposed engine design.

• Access: The spark plugs on a Boxer engine are located on the sides of the engine, making access a bit tighter than a traditional V-engine or inline design. You may need to remove or relocate certain components (like the air intake on one side) to gain adequate access.
• Coil-on-Plug Removal: The 2025 Outback uses a coil-on-plug (COP) ignition system. Each spark plug has its own ignition coil mounted directly on top. To remove, carefully disconnect the electrical connector, then unbolt the coil (usually a 10mm bolt) and pull it straight up and off the spark plug. Use a gentle rocking motion if it's stubborn.
• Anti-Seize Debate: There's ongoing debate about using anti-seize on spark plug threads. Most modern spark plugs, especially those from NGK, have a special coating on the threads to prevent seizing. Applying additional anti-seize can actually alter the torque readings, leading to over-tightening and potential damage to the cylinder head threads. Subaru and NGK generally recommend not using anti-seize on their coated plugs. If you choose to use it, apply a very thin coat and reduce the torque spec by approximately 10-20%.
• Dielectric Grease on Boots: A small dab of dielectric grease inside the spark plug boot (the part that connects to the ceramic insulator of the spark plug) can aid in sealing out moisture and preventing the boot from sticking to the plug over time. It also helps with easier removal in the future.

Known Issues (Applicable to 2025 Subaru Outback)

Fortunately, the FB25 and FA24F engines in the Subaru Outback do not suffer from widespread "known issues" related to spark plugs comparable to the infamous Ford 3-valve two-piece plug breakage or specific ionization-sensing coil problems found in some GM engines.

However, general precautions always apply:

• Cross-threading: Always start spark plugs by hand to ensure they thread in smoothly. If you feel resistance, stop immediately and re-align. Cross-threading can severely damage the cylinder head threads.
• Over-tightening: Exceeding the specified torque can strip the threads or, in extreme cases, crack the cylinder head. Under-tightening can lead to the plug backing out, causing misfires and potential damage to the coil.

Need plugs replaced? Find a shop on Repairius.