2018 Subaru Crosstrek Spark Plug Type and Gap Guide

Quick Reference

Why the Right Plug Matters

Choosing the correct spark plug for your 2018 Subaru Crosstrek is crucial for optimal engine performance, fuel economy, and longevity. Using the wrong plug can lead to misfires, reduced power, increased emissions, and even engine damage.

Heat Range

Spark plugs are designed with a specific "heat range," which refers to their ability to dissipate heat from the combustion chamber. A plug that's too "hot" (dissipates less heat) can overheat, leading to pre-ignition and detonation, which are extremely damaging to an engine. A plug that's too "cold" (dissipates too much heat) can foul with carbon deposits, causing misfires and poor performance. The OEM-specified plugs are precisely engineered for the FB20D engine's operating temperatures.

Electrode Metal

Spark plugs come with various electrode materials, each offering different durability and performance characteristics:

• Iridium: The most common type for modern vehicles like your Crosstrek. Iridium plugs feature extremely fine center electrodes, promoting a strong, consistent spark. They offer exceptional durability and a long service life, typically 60,000 to 100,000 miles. Both the OEM Subaru and recommended NGK/Denso plugs for your Crosstrek are iridium.
• Platinum: Another long-lasting option, often found in original equipment applications. Platinum plugs also offer good durability, typically lasting 60,000 miles or more. While not the primary OEM choice for your Crosstrek, they are a reliable alternative in some applications.
• Copper: The oldest and most conductive material. Copper plugs have a thicker center electrode and a shorter lifespan, usually requiring replacement every 15,000 to 30,000 miles. Due to their rapid wear, they are generally not suitable for modern engines that require extended service intervals.

How to Gap a Spark Plug

The spark plug gap is the distance between the center and ground electrodes. An incorrect gap can lead to misfires or a weak spark. While most iridium and platinum plugs come pre-gapped from the factory, it's always a good idea to double-check before installation.

For your 2018 Subaru Crosstrek, the recommended gap is 0.043 inches (1.1 mm).

To check and adjust the gap:

1. Use a wire-style feeler gauge: This type of gauge is crucial for modern plugs with delicate electrodes, as a ramp-style gauge can damage the iridium or platinum tip.
2. Slide the appropriate wire into the gap: It should have a slight drag. If it slides too easily, the gap is too wide. If it doesn't fit, the gap is too narrow.
3. Adjust carefully: If the gap needs adjustment, gently bend the ground electrode. Use a proper gapping tool that leverages the side of the plug, not the delicate center electrode. Be extremely careful not to touch or damage the iridium tip. A common mistake is using pliers directly on the ground electrode, which can easily crack the porcelain insulator.

Replacement Procedure Tips

Replacing spark plugs on the Subaru FB20D engine in your Crosstrek can be a bit challenging due to the horizontally opposed "boxer" engine design, which places the plugs deep in the engine bay.

1. Access: You will need to remove the airbox and potentially the battery on one side for better access. On the driver's side, the coolant reservoir might need to be moved. Long extensions (around 6 inches and 10 inches), a universal joint, and a swivel spark plug socket are highly recommended.
2. Coil-on-Plug Removal: Your Crosstrek uses a coil-on-plug (COP) ignition system. To remove the ignition coils, carefully disconnect the electrical connector by pressing the tab and pulling. Then, unbolt the coil (typically a 10mm bolt) and pull it straight up and out. Apply a small amount of dielectric grease inside the boot of the new coil before reinstallation to help seal out moisture and ease future removal.
3. Anti-Seize Debate: While many technicians traditionally use anti-seize on spark plug threads, Subaru (and NGK/Denso for their plated plugs) specifically recommends against it. Modern spark plugs often have a special coating on the threads that acts as an anti-seize agent. Applying additional anti-seize can alter the friction, leading to over-tightening and potentially stripping the cylinder head threads or breaking the plug.
4. Torque is Critical: Always use a calibrated torque wrench to tighten the new spark plugs to the specified 15.2 lb-ft (20.6 Nm). Under-tightening can cause cylinder compression leaks and plug overheating, while over-tightening can damage the spark plug, cylinder head threads, or the engine itself.
5. Cleanliness: Before removing the old plugs, use compressed air to blow out any debris from around the spark plug wells. This prevents dirt and grime from falling into the combustion chamber once the old plug is removed.

Known Issues (Not Applicable for 2018 Crosstrek FB20D)

Fortunately, the 2018 Subaru Crosstrek with the FB20D engine does not have widely documented common spark plug issues like the two-piece plug breakage seen in some Ford 3-valve engines or unique ionization-sensing coil problems like certain GM 5.3L engines. As long as you use the correct OEM or recommended equivalent plugs and follow proper installation procedures, you should experience reliable performance.

Need plugs replaced? Find a shop on Repairius.