2015 Subaru Forester Spark Plug Type & Gap

Quick reference

Why the right plug matters

Choosing the correct spark plug for your 2015 Subaru Forester is critical for optimal engine performance, fuel efficiency, and longevity. Spark plugs are more than just simple igniters; they are carefully engineered components that must operate within a specific heat range and utilize appropriate electrode materials to suit your engine's design and operating conditions.

Heat Range: This refers to the plug's ability to dissipate heat. A "cold" plug dissipates heat quickly and is suitable for high-performance or turbocharged engines (like the Forester's 2.0L turbo) to prevent pre-ignition. A "hot" plug retains more heat, ideal for engines that run at lower temperatures to prevent fouling. Using a plug with an incorrect heat range can lead to issues like misfires, reduced power, and even engine damage.

Electrode Metal:

• Iridium: This is the most common and recommended material for modern vehicles like your 2015 Forester. Iridium plugs offer exceptional durability and a fine-wire electrode, which provides a very efficient spark. They have a lifespan of 60,000 to 100,000 miles.
• Platinum: Platinum plugs are also durable, lasting around 50,000 to 60,000 miles. They are a good step up from copper but typically not on par with iridium for longevity or performance in newer, high-tech engines.
• Copper: While excellent conductors, copper plugs have a much shorter lifespan (typically 20,000 to 30,000 miles) due to the softer nature of the material. They are usually found in older vehicles or those with less demanding ignition systems.

Your 2015 Subaru Forester, whether equipped with the 2.5L naturally aspirated or the 2.0L turbocharged engine, uses iridium-tipped spark plugs from the factory, specifically NGK, for their long life and consistent performance.

How to gap a spark plug

While many modern iridium spark plugs come pre-gapped from the factory and should generally not be adjusted, it's always a good practice to verify the gap against the manufacturer's specification before installation. If adjustment is necessary, proceed with extreme caution, especially with fine-wire iridium plugs, as the delicate electrode can be easily damaged.

To gap a spark plug:

1. Use the correct tool: A wire-type feeler gauge is preferred over a ramp-style coin gap tool, especially for fine-wire electrodes, as it reduces the risk of damaging the tip.
2. Verify the gap: Carefully slide the correct thickness wire gauge between the center and ground electrodes. There should be a slight drag.
3. Adjust (if necessary): If the gap is too small, gently pry the ground electrode only using the gapping tool's adjustment slot. If the gap is too large, gently tap the ground electrode on a hard, non-marring surface to close it. Never pry or tap on the center electrode.

For your 2015 Forester, the gap specifications are very precise. For the 2.5L engine, it