Subaru Legacy: EJ25 DOHC External Head Gasket Coolant Leak

The EJ25 DOHC engine fitted to BL/BP GT and outgoing BM/BR models suffers a well-documented failure of the composite head gasket at the external coolant passages on the exhaust side of each cylinder head. The gasket face breaks down between the coolant jacket and the outside of the block, allowing coolant to seep externally rather than into the combustion chamber. This makes detection harder — there is often no hydrocarbon contamination in the coolant and no white smoke — while coolant loss is slow and progressive. Left untreated the engine overheats and warps the aluminium head, turning a gasket job into a head-resurfacing or replacement job. Considered the single most common mechanical failure on the EJ25 platform.

• Slow coolant loss requiring top-up every 1000–3000 km with no visible puddle under the car
• Brown or orange crusty residue at the head gasket joint line on the outside of the engine block
• Temperature gauge creeping higher than normal on long highway runs or in traffic
• Sweet coolant smell from the engine bay after a run

With engine at operating temperature, inspect the head-to-block join on both cylinder banks for brown or orange crystallised coolant residue. Check coolant reservoir level trend over 500 km. Check for sweet smell from engine bay with no visible external leak. If a workshop inspection is possible: Pressure-test the cooling system cold and watch for slow pressure drop.

Parts involved: Head gasket.

$2,200 to $4,500 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “Has the head gasket ever been replaced, and if so when and by which workshop?”
• “Can you show me the coolant reservoir — is it at the same level as last time it was checked?”
• “Has the car ever overheated or been driven while hot?”

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.