Subaru Legacy: EJ20 Head Gasket Inter-Cylinder Seepage (Cylinders 2–3)

The EJ20 flat-four engine fitted to BL/BP base and 2.0R variants is prone to a distinct head gasket failure mode that differs from the EJ25 external leak. The gasket fails between cylinders 2 and 3 on the same head, allowing combustion gases and oil to migrate across the fire ring. This results in a misfire, contaminated oil, and eventually oil mixing into the coolant passages. Because the leak is internal, owners may not see external residue and may misdiagnose the misfire as ignition-related before cylinder-wash and contaminated oil reveal the true cause. OEM-spec composite gaskets are considered the root cause; multi-layer steel (MLS) upgrades with re-torqued or resurfaced heads are the accepted fix.

• Persistent misfire on cylinder 2 or 3 that does not resolve after replacing plugs and coils
• Milky or caramel-coloured residue on the underside of the oil filler cap
• Coolant loss with no external seepage visible anywhere on the engine
• Blue-white smoke from the exhaust on cold start, clearing as engine warms

1. 1

   Pull the oil dipstick and look for a milky or frothy emulsion indicating coolant contamination.

2. 2

   Check for misfire codes on cylinders 2 or 3 (P0302/P0303).

3. 3

   Perform a block-test (combustion gas sniffer) on the coolant reservoir.

4. 4

   Remove the oil filler cap and inspect the underside for mayo-like residue.

Parts involved: Head gasket.

$1,800 to $3,500 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 engine ever had a misfire, and what was the diagnosis?”
• “When was the oil last changed, and was the oil normal colour?”
• “Has the coolant reservoir level been dropping?”

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.