Parts for your 2018 Subaru Forester-Head gasket

2018 Subaru Forester head-gasket — what it does and when to sort it

Yes, the 2018 Subaru Forester uses cylinder head gaskets. This is specified in Subaru’s Factory Service Manual for the 2018MY Forester (Engine/Mechanical sections for FB25 and FA20F) and reflected in Subaru’s genuine parts catalogues, which list the multi‑layer steel (MLS) cylinder head gasket for both engines. Being a boxer (horizontally opposed) four, the Forester has two cylinder heads and therefore two head gaskets—one per bank.

The head gasket’s job is to seal the combustion chambers while keeping engine oil and coolant in their proper passages. On the 2018 Forester’s FB25 2.5‑litre and FA20F 2.0‑litre turbo engines, the MLS design provides robust sealing under thermal cycling, boost (on the FA20F), and the unique clamping pattern of a flat-four. When healthy, it maintains compression, prevents coolant and oil from mixing, and keeps temperatures stable—key to smooth running and good fuel economy.

Head gaskets aren’t a routine service item, they’re replaced only if there are symptoms or test results pointing to a fault. Owners and workshops commonly watch for:

• Unexplained coolant loss, bubbles in the overflow bottle, or overheating under load
• Milky residue on the oil cap or dipstick, or sweet-smelling white exhaust steam once warm
• Rough cold starts or a misfire on one bank

If replacement is required, best practice (as outlined in Subaru service literature) is to use OEM MLS gaskets, fit new head bolts where specified (torque‑to‑yield on many builds), and follow the multi‑stage torque‑angle sequence precisely. Cylinder head flatness should be measured and the surface lightly machined if out of spec. It’s wise to renew the thermostat, cap, and any tired hoses, and to refill with the correct Subaru long‑life coolant. Given the FB/FA timing chains, there’s no belt service to bundle in, but cam carrier and front cover seals are worth attention while access is open.

For day‑to‑day care, sticking to the coolant change interval in the owner’s manual, keeping the cooling system clean, and using the right spec oil helps the gasket live a long, drama‑free life. Regular under‑bonnet checks for coolant level and any external staining go a long way to catching issues early, especially on vehicles doing big kilometres or frequent towing.

• Popular questions

How can someone spot an early head-gasket issue on a 2018 Forester?
Early clues include slow coolant loss with no obvious leaks, a cooling system that pressurises quickly from cold, or fine bubbles in the overflow. A chemical block test or a cooling‑system pressure test can confirm suspicions. Oil that turns milky or exhaust that steams sweetly after warm‑up are later signs.

Do the FB25 2.5‑litre and FA20F 2.0‑litre turbo differ for head-gasket reliability?
Both use MLS gaskets per Subaru technical documentation. The turbo FA20F sees higher cylinder pressures and heat, so maintenance of cooling and tune quality is more critical. With correct fluids, proper warm‑up, and factory torque procedures, both engines have solid sealing performance.

What does a head-gasket job involve and how long does it take?
It’s a substantial workshop task: intake and exhaust removal, timing lock‑down, cam carrier access, head removal, inspection, and precise reassembly with torque‑angle stages. Many workshops allow one to two days depending on parts, machining needs, and whether ancillary seals and cooling components are renewed.