Parts for your 2018 Subaru Forester-Spark plugs

2018 Subaru Forester Spark Plugs — What They Do and When to Change Them

Per the 2018 Subaru Forester Owner’s Manual and Subaru’s service information (STIS), the Forester’s petrol engines — the 2.5‑litre FB25 and 2.0‑litre turbo FA20F — use iridium spark plugs with coil‑on‑plug ignition. Diesel variants (EE20) don’t use spark plugs at all, they rely on compression ignition with glow plugs for cold starts, so spark‑plugs aren’t relevant on those models.

For any 2018 Forester running on petrol, spark plugs are a quiet hero. Each plug ignites the air–fuel mix inside the boxer engine’s cylinders, keeping starts crisp, idle smooth, power on tap, and fuel economy in check. Subaru specifies long‑life iridium plugs for durability and consistent spark under Aussie and Kiwi conditions.

Service guidance from Subaru’s manuals indicates replacement intervals vary by engine and market. As a rule of thumb, owners can expect:

• 2.5i (FB25) petrol: long‑life interval — plan inspection at major services and replacement around the 100,000 km mark, per the vehicle’s service book.
• 2.0XT (FA20F) turbo petrol: harsher on plugs — expect shorter intervals (often around 60,000–100,000 km). Follow the VIN‑specific schedule in the owner’s manual.

Between changes, a workshop should check for oil or coolant contamination, cracked insulators, worn electrodes, and correct torque on refit. The factory gap is typically pre‑set for iridium plugs, most Subaru sources advise not regapping iridium types, so correct part numbers matter more than fiddling with the gap.

Signs the Forester may be due sooner include:

• Hard starts, rough idle or a bit of a stumble under load
• Heavier fuel use or sluggish performance compared with usual
• Misfire codes and a flashing or steady check‑engine light

Good workshops replace plugs in sets of four, use the specified iridium plugs for the exact engine code, and pair the job with new coil boots if they’re tired. Under the bonnet, coil‑on‑plug units sit right on top of each plug, so keeping moisture out and using anti‑seize only if Subaru specifies it are part of doing it right.

If the vehicle is a 2018 Forester diesel, spark‑plugs don’t come into the picture. Diesel combustion doesn’t need a spark, it compresses air until it’s hot enough to ignite diesel, with glow plugs simply helping with cold starts.

Popular questions about 2018 Subaru Forester spark plugs

How often should spark plugs be replaced on a 2018 Forester?
Service schedules differ by engine and market. The 2.5i petrol typically runs long‑life intervals around the 100,000 km region, while the 2.0XT turbo is often earlier, about 60,000–100,000 km. Always follow the owner’s manual or service book for the exact interval tied to the VIN and driving conditions.

What type of spark plugs does it use?
Subaru specifies iridium plugs matched to the engine code (FB25 or FA20F). The plugs are factory pre‑gapped, most Subaru service information recommends not regapping iridium plugs. Using the correct OEM‑equivalent part number is the safest bet.

What symptoms point to worn plugs on a Forester?
Look for harder cold starts, rough idle, hesitation under load, poorer fuel economy, or an engine light with misfire codes. Any of those are a nudge to have the plugs and ignition system checked during the next service.