2015 Subaru Crosstrek Spark Plug Type & Gap

Quick Reference

Why the right plug matters

Choosing the correct spark plug for your 2015 Subaru Crosstrek 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 a specific heat range, which dictates how well they dissipate heat from the combustion chamber. A plug that is too "hot" (dissipates heat slowly) can lead to pre-ignition and detonation, damaging your engine. A plug that is too "cold" (dissipates heat too quickly) can cause carbon fouling, leading to misfires and poor performance. Your Crosstrek's FB20D engine is designed for a specific heat range, and straying from the OEM specification can have detrimental effects.

• Electrode Metal: Modern spark plugs utilize various precious metals for their electrodes to enhance durability and performance. For your Crosstrek, the OEM plugs are iridium. Iridium plugs offer superior longevity and a finer electrode tip compared to platinum or traditional copper plugs, leading to a more consistent and powerful spark over a longer service life. While copper plugs offer excellent conductivity, their shorter lifespan makes them unsuitable for modern engines with extended service intervals like your Crosstrek.

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 double-check the gap before installation, especially if the plug has been dropped or had its packaging damaged. For your 2015 Subaru Crosstrek, the recommended gap is 0.043 inches (1.1 mm).

To gap a spark plug, you'll need a spark plug gapping tool – a wire-type or coin-style tool is common. Carefully insert the correct feeler gauge or wire into the gap between the center and ground electrodes. If the gap is too small, gently bend the ground electrode outwards. If the gap is too large, carefully tap the ground electrode on a hard surface to close it slightly. Always be gentle, as excessive force can damage the fragile iridium tip.

Replacement procedure tips

The 2015 Subaru Crosstrek with the 2.0L FB20D engine utilizes a coil-on-plug ignition system, meaning each spark plug has its own dedicated ignition coil. This simplifies the replacement process compared to older distributor-based systems.

1. Access: The spark plugs on your Crosstrek are located on the sides of the engine, under the coil packs. You will likely need to remove the airbox and potentially a few other components to gain adequate access to all four plugs.
2. Coil-on-Plug Removal: Carefully disconnect the electrical connector from each ignition coil. Then, unbolt the coil (typically one or two small bolts) and gently pull the coil straight up and off the spark plug. Avoid yanking or twisting, as this can damage the coil boot or the plug itself.
3. Anti-Seize Debate: There is ongoing debate about using anti-seize compound on spark plug threads. For modern plugs with plated shells, manufacturers often advise against anti-seize, as it can alter the torque readings and potentially lead to over-tightening or incorrect heat transfer. Subaru, like many other manufacturers, generally recommends installing plugs clean and dry, relying on the plug's plating to prevent seizing. Refer to your owner's manual or a factory service manual for the definitive recommendation for your specific vehicle.
4. Dielectric Grease: It's a good idea to apply a small amount of dielectric grease inside the spark plug boot (the part that connects to the top of the spark plug). This helps to seal out moisture, prevent corrosion, and makes future removal easier.
5. Torque: Always, always torque your spark plugs to the manufacturer's specification: 15.0 lb-ft (20.3 Nm) for your Crosstrek. Over-tightening can damage the plug or cylinder head threads, while under-tightening can lead to blow-by and misfires. A torque wrench is an essential tool for this job.

Known Issues

Fortunately, the 2015 Subaru Crosstrek's FB20D engine does not have widespread, well-documented catastrophic spark plug issues like the infamous Ford 3-valve 2-piece plug breakage or GM's ionization-sensing coil problems. However, general spark plug maintenance considerations still apply:

• Fouling: Neglecting oil changes or having internal engine issues (like worn piston rings or valve guides) can lead to oil fouling of the spark plugs. Similarly, running too rich or having a persistent misfire can lead to carbon fouling. Regular maintenance and addressing any engine warnings promptly will help prevent these issues.
• Cross-Threading: Be extremely careful when installing new spark plugs. Always start them by hand to ensure they thread smoothly into the cylinder head. Cross-threading aluminum cylinder heads is an expensive mistake.

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