2015 Subaru Outback Spark Plug Specifications

Quick Reference

Why the Right Plug Matters

Choosing the correct spark plug is critical for engine health and performance. The two primary considerations are heat range and electrode material.

Heat Range: A spark plug's heat range determines how quickly it dissipates heat from the combustion chamber. A "hot" plug transfers heat slowly, burning off carbon deposits at low speeds, while a "cold" plug transfers heat quickly to prevent overheating and pre-ignition under high load. The 2015 Outback's engines are designed for specific heat ranges to ensure optimal combustion.

Electrode Material:

• Iridium: The OEM choice for the 2015 Outback, iridium plugs have an extremely high melting point and offer the best performance and longevity, often lasting up to 100,000 miles.
• Platinum: A good alternative to iridium, platinum plugs offer a long service life and consistent performance, though typically with a shorter lifespan than iridium.
• Copper: While excellent conductors, copper plugs have the shortest lifespan and are not recommended for the 2015 Outback, as they would be a significant downgrade from the factory-installed iridium plugs.

How to Gap a Spark Plug

Properly gapping your spark plugs is essential for a strong, consistent spark. Iridium and platinum plugs are often pre-gapped, but it's always wise to verify.

1. Use a Feeler Gauge: A wire-style or feeler gauge is the best tool for the job. Avoid coin-style gappers, as they can damage the delicate iridium tip.
2. Check the Gap: Gently slide the appropriate gauge wire between the center and ground electrodes. It should create slight drag without forcing it.
3. Adjust if Necessary: If the gap is too wide or narrow, gently bend the ground strap with a gapping tool. Never pry against the center electrode.

Replacement Procedure Tips

The 2015 Subaru Outback features a coil-on-plug ignition system, which simplifies the replacement process compared to older distributor-based systems.

• Coil-on-Plug Removal: Each spark plug has its own ignition coil directly on top. Disconnect the electrical connector, unbolt the coil (typically a single 10mm or 12mm bolt), and gently twist and pull it straight up to remove it.
• The Anti-Seize Debate: Modern NGK and Denso plugs often have a special trivalent plating that provides anti-seize properties. Applying additional anti-seize can act as a lubricant, leading to over-torquing and potential damage to the plug or cylinder head. It is generally not recommended unless specified by the plug manufacturer.
• Dielectric Grease: Apply a small amount of dielectric grease to the inside of the spark plug boot before reinstalling the ignition coil. This prevents the boot from sticking to the plug and protects against moisture and corrosion.

Known Issues

Fortunately, the 2015 Subaru Outback and its FB25 and EZ36 engines are not known for widespread spark plug-related issues like the Ford 3-valve breakage or GM ionization-sensing problems. The primary challenge with these boxer engines is access, particularly for the plugs on the driver's side, which may require removing the battery and other components for clearance. Following the correct torque specifications is crucial to prevent stripped threads in the aluminum cylinder heads.

Need your plugs replaced? Find a shop on Repairius.