Subaru Forester: EJ253 Internal Head Gasket Failure – Combustion Gas or Coolant Bypass

In its more severe form, the EJ253 head gasket fails internally, allowing combustion gases to pressurize the cooling system or coolant to enter the combustion chamber. Coolant ingress burns as white, sweet-smelling exhaust smoke, while pressurized combustion gases cause the coolant overflow tank to bubble and purge coolant. Overheating events resulting from coolant loss can warp the aluminium cylinder heads, requiring machining or replacement in addition to the gasket repair.

• White or sweet-smelling exhaust smoke that persists after the engine is fully warm
• Coolant level falling with no visible external leak
• Bubbling or gurgling in the coolant overflow reservoir at idle
• Milky or frothy contamination on the oil dipstick or under the oil filler cap
• Temperature gauge climbing above normal or overheating warning activating

Allow the engine to reach full operating temperature then shut it off. With a cold engine idling, watch for white exhaust smoke that does not clear after two minutes. Use a combustion leak test kit (block tester with combustion dye) on the coolant reservoir filler neck to detect exhaust gas in the coolant. If a workshop inspection is possible: Once cool, remove the coolant overflow cap and check for oily contamination or a mayonnaise-like emulsion on the cap or tank neck.

Parts involved: Head gasket.

$2,200 to $5,000 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 this vehicle ever overheated, and if so, were the cylinder heads inspected or skimmed?”
• “Has a combustion leak test (block test) ever been performed on the cooling system?”
• “Is there a repair receipt showing head gasket replacement, and which gasket set was used?”

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.