Parts for your 2003 Subaru Forester-Head gasket

2003 Subaru Forester head gasket: what it does, what goes wrong, and how to look after it

The 2003 Subaru Forester runs the 2.5‑litre EJ25 flat‑four, which absolutely uses cylinder head gaskets between each cylinder head and the engine block. This isn’t optional hardware. Subaru’s factory service manual for the 2003 Forester (engine section covering the cylinder head) specifies the head gasket and its torque sequence, and the Subaru parts catalogue lists the head gasket as a distinct service part for the EJ25. Subaru also issued technical guidance in the early 2000s recommending its cooling system conditioner for minor external coolant seepage on SOHC EJ25 engines—another clear pointer that head gaskets are part of the platform and a recognised service consideration.

On this Forester, the head gasket’s job is to seal three things at once: high‑pressure combustion in each cylinder, engine oil passages, and coolant passages. The gasket is a precision, multi‑layer steel design that sits between the aluminium head and the block. When it’s healthy, the engine runs cool, clean and efficient. When it’s tired or damaged, it can weep coolant externally, allow combustion gases into the cooling system, mix oil and coolant, or cause overheating under load.

Smart maintenance keeps trouble at bay. At every service, a technician should:

• Check for dried coolant “crust” or dampness at the head‑to‑block seam, especially low on the head.
• Pressure‑test the cooling system and cap, and verify the coolant’s condition and level.
• Look for misfires on cold start, sweet exhaust odour, or bubbles in the overflow bottle.
• Use the correct Subaru‑spec coolant