Parts for your 2018 Subaru Impreza-Head gasket

2018 Subaru Impreza head gasket — what it does, how it fails, and when to replace

Based on Subaru’s Global Service Manual for MY2018 Impreza (FB-series engine), the Subaru FAST electronic parts catalogue, and widely used workshop references such as Haynes, the 2018 Subaru Impreza is fitted with a cylinder head gasket. It’s an MLS (multi‑layer steel) gasket that sits between each cylinder head and the engine block on the 2.0‑litre FB20 boxer engine.

The head gasket’s job is simple but critical: it seals combustion pressure in the cylinders while keeping engine oil and coolant in their own passages as they travel between the block and heads. On the flat‑four FB20, there are two gaskets (one per bank). Subaru moved to robust MLS designs and improved cooling passages on the FB engines, so head‑gasket dramas are far less common than on some older EJ motors, but any gasket can fail if the engine overheats or maintenance is skipped.

For owners, prevention is the best play. Keep the cooling system in top nick: use the correct Subaru‑spec long‑life coolant, maintain the radiator cap and hoses, and replace coolant at the interval in the owner’s manual. Avoid running low on coolant and fix any leaks quickly. Regular oil changes matter too, because clean oil helps the gasket live a long life. Watch temperatures under load (towing, long climbs) and don’t ignore the temp warning light — overheating is the head gasket’s worst enemy.

Common warning signs include:

• Unexplained coolant loss or a sweet smell after shutdown
• Overheating, bubbles in the overflow bottle, or pressurised hoses when cold
• Milky oil, white exhaust steam once warm, or a rough cold start
• Poor cabin heater output alongside rising temperature

If replacement is needed, it’s a substantial job that often involves removing the engine on a Subaru boxer. A quality repair will use OEM‑spec MLS gaskets, new head bolts (they’re torque‑to‑yield), correct surface prep and flatness checks, precise torque‑angle procedures, and fresh fluids. It’s smart to do both gaskets while the engine is out, and to renew the thermostat, small coolant hoses, and any weeping seals. The FB20 uses a timing chain, not a belt, but the tech should still inspect chain guides, the water pump, and front covers while in there. After the first heat cycle, recheck for leaks and confirm the cooling system is properly bled. Done right, a new set of gaskets should deliver years and many kilometres of trouble‑free motoring under the bonnet of a 2018 Impreza.

Popular questions

Do 2018 Subaru Impreza models still have head‑gasket problems like older Subarus?
Not typically. The FB20’s MLS gaskets and cooling design greatly reduced the historic issues seen on some EJ engines. With proper coolant and oil servicing, failures on 2018 models are relatively uncommon.

What are early signs of a failing head gasket on a 2018 Impreza?
Look for rising temps, coolant loss with no obvious leak, bubbles in the overflow bottle, a sweet smell, persistent white steam from the exhaust when warm, or milky residue on the oil cap. Any of these warrant a pressure test and chemical block test.

Should both head gaskets be replaced at the same time?
Yes, that’s generally recommended. Because access on the boxer is similar for both sides and the engine is often removed, doing both gaskets together is the most reliable and cost‑effective approach.