Parts for your 2018 Subaru Legacy-Head gasket

2018 Subaru Legacy head gasket — what it does and how to look after it

Yes, the 2018 Subaru Legacy uses a head gasket. This is documented in the Subaru Factory Service Manual for the 2018 Legacy/Outback (FB25 and EZ36 engine sections), which details the multi‑layer steel (MLS) cylinder head gasket and the torque‑angle procedure for the head bolts. The official Subaru parts catalogue for the 2018 Legacy also lists cylinder head gaskets for both the 2.5‑litre FB25 and 3.6‑litre EZ36 engines. Independent workshop references such as the Haynes Subaru Legacy/Outback 2010–2019 manual cover the same component and service steps.

On a 2018 Legacy, the head gasket sits between the engine block and each cylinder head (it’s a flat‑four or flat‑six, so there are two). Its job is to keep combustion pressure sealed while also keeping engine oil and coolant in their own passages. An MLS gasket is used for durability and heat cycling, especially important in Subaru’s boxer layout where each bank runs horizontally under the bonnet.

This gasket isn’t a routine service item, it’s replaced when there’s a fault or during major engine work. Owners get the best life out of it by sticking to proper cooling‑system maintenance. That means using the correct Subaru‑approved long‑life coolant, keeping the system bled of air, replacing the radiator cap if it’s weak, and sorting any overheating straight away. Overheating is the quickest way to stress a head gasket.

• Common warning signs: unexplained coolant loss, bubbling in the overflow bottle, white steam from the exhaust after warm‑up, sweet odour, milky residue under the oil filler cap, misfires at start‑up, or an external coolant weep along a head‑to‑block seam.
• Preventative tips: keep the cooling fans, thermostat and water pump healthy, don’t mix coolant types, use demineralised water if topping up, follow the service schedule for coolant change intervals noted in the owner’s manual.

If replacement is needed, be aware it’s a fairly involved job on the FB/EZ engines. Workshop best practice is to remove the engine, do both banks together, check head and block surfaces for flatness, use new head bolts where specified, and follow the factory multi‑stage torque‑angle sequence. It’s also the right time to refresh cam and front crank seals, timing chain guides (inspection on FB25), and all coolant hoses. A proper repair will include fresh oil and coolant, careful bleeding, and post‑repair checks for combustion gases in the cooling system. Done right with OEM‑quality parts, a new MLS gasket should give many more years and kilometres of reliable service on Aussie and Kiwi roads.

Q: Do 2018 Subaru Legacy models still have head gasket problems?

They’re far less common than on older EJ engines. The 2018 FB25 and EZ36 use MLS gaskets and improved sealing. Failures can still happen if the car overheats or the cooling system is neglected, but with proper servicing many owners never see a head gasket issue.

Q: What are early signs of a head gasket issue on a 2018 Legacy?

Look for slow coolant loss with no obvious leak, bubbles in the overflow after a drive, persistent sweet exhaust vapour once warm, or a misfire on cold start. Oil that goes milky or a rising temperature gauge under load are also red flags worth checking promptly.

Q: Should both head gaskets be replaced at the same time?

On Subaru boxer engines it’s generally recommended. With the engine out, labour overlaps heavily, doing both banks, resurfacing as needed, and renewing bolts gives balanced compression and long‑term reliability.