Parts for your 2004 Subaru Forester-Head gasket

2004 Subaru Forester head gasket — what it does and how to look after it

Yes, a head gasket is absolutely used on the 2004 Subaru Forester. Technical references including the 2004 Subaru Forester Service Manual (Engine, EJ25 series), and Subaru Technical Service Bulletin 09-36-03 regarding cooling system conditioner, confirm the EJ25’s horizontally opposed (boxer) engine employs a cylinder head gasket on each bank to seal combustion, oil and coolant passages. Industry guides such as ALLDATA/Mitchell and Haynes also document Forester head-gasket service procedures for this model year.

On a 2004 Forester, the head gasket sits between the aluminium cylinder head and the engine block, and there’s one per side. Its job is simple but critical: keep high-pressure combustion in, and keep coolant and oil in their own lanes. Because the EJ25 runs alloy heads and sees big temperature swings, the gasket cops a hard life. Early-2000s composite gaskets were known to seep externally, later multi-layer steel (MLS) designs are the preferred fix when it’s time to rebuild.

If the Forester’s due for a cooling system service, it’s wise to think of the head gasket as part of the wider system’s health. Use the correct Subaru-approved coolant and, where specified by Subaru’s bulletin, the cooling system conditioner. Keep coolant changes on schedule (about every 2 years or 40,000–50,000 km), check the radiator cap, and make sure the system is bled properly via the header tank with the heater on. A tidy cooling system helps the gasket live a long, drama-free life.

Common warning signs include a sweet coolant smell under the bonnet, dampness at the head/block join, bubbles in the overflow, unexplained coolant loss, overheating, or milkiness under the oil filler cap. Catching issues early can save the bottom end from bearing damage.

When replacement is on the cards, most workshops recommend engine-out for easier access on a boxer. It’s smart to do both head gaskets, machine and pressure-test the heads, and refresh the timing belt, water pump, idlers, thermostat, cam/crank seals and hoses while it’s apart. Use the updated OEM-style MLS gaskets, follow the exact torque-and-angle sequence from the service manual, and replace head bolts if they’re out of spec. Done right, the repair is a solid long-term fix and the Forester’s good for many more kilometres.

• Pro tip: small external weeps may be managed short-term with the Subaru conditioner, but persistent leaks or overheating call for gasket replacement.

Popular questions

What are the early signs of a failing head gasket on a 2004 Forester?
Look for an external coolant weep at the head/block seam, sweet smells, bubbles in the overflow after a spirited drive, rising temps on long climbs, or a heater that goes cold then hot. Milky residue under the oil filler cap or white exhaust smoke on a warm engine are bigger red flags.

If any of these show up, stop driving hard, check coolant level once the engine’s cold, and book a pressure test and chemical block test.

Which head gasket should be used when replacing?
Go for the later multi-layer steel (MLS) style with quality coatings, matched to the exact EJ25 variant. Pair it with fresh head bolts (if length or thread condition is marginal), genuine-spec coolant, and follow the service manual’s torque-angle sequence. That combo solves most repeat-leak stories on these engines.

Is the Subaru cooling system conditioner worth using?
Per Subaru TSB 09-36-03, the conditioner can reduce minor external seepage on Phase II EJ25s. It’s not a cure for a blown gasket, but it’s a useful preventative when used with the correct coolant during routine services. If there’s overheating or combustion gases in the coolant, skip the bandaids and schedule proper repairs.