MajorCommonEngine

Subaru STI: EJ20/EJ25 Head Gasket Failure

EJ20/EJ25 Head Gasket Failure is a common engine fault on the Subaru STI on the 2001–2014 cars, and we rate it major. Putting it right costs ≈A$1,660 to ≈A$4,140 at independent workshop rates, shown as an approximate guide in Australian dollars. Below is what goes wrong, the symptoms to notice on a test drive, where to look, and what to ask the seller before you hand over any money. It is one of 33 documented faults on the Subaru STI.

Vehicle: Subaru STI
Engine: EJ20 / EJ25
Years: 2001–2014
Fuel: petrol
System: Engine

This page covers the Subaru STI as a model. Some faults only affect particular engines or build years — enter a plate below to narrow the list to one car.

All Subaru STI faults33 documented faults on this model

What you are looking at

What goes wrong

The EJ-series engines use a multi-layer steel (MLS) head gasket that seals between the aluminium cylinder head and the iron or aluminium block. Thermal cycling between the two dissimilar metals causes differential expansion rates that progressively fatigue the gasket fire-ring. On turbocharged applications, elevated coolant temperatures from heat soak, stuck thermostats, or coolant system neglect accelerate this failure. EJ25 engines (2.5 litre, used in the WRX from 2006 and in later STI models) are reported as more prone than EJ20 units because the larger bore leaves less metal between cylinders. Failure modes include external coolant leaks at the block-head joint, internal coolant-to-oil mixing, and combustion gas leaks that cause coolant system pressurisation. Many examples have had head gaskets replaced once already by 150,000 km.

What you would notice

Coolant loss without visible external leak
White smoke from exhaust at operating temperature
Creamy white emulsion on oil filler cap or dipstick
Coolant reservoir bubbling at operating temperature
Engine overheating or temperature gauge fluctuation
Sweet smell from engine bay or exhaust

How to check it

Where to look. Cylinder head gasket — both left and right banks of the horizontally-opposed engine

Check the oil filler cap and dipstick for any creamy or mayonnaise-like emulsion. A combustion leak tester (block tester with chemical dye) should be used on the coolant reservoir. Inspect the engine bay and block-head junction for any coolant residue or mineral deposits. If a workshop inspection is possible: With engine at operating temperature, remove the radiator cap (engine cold first) and look for bubbling in the coolant — combustion gases entering the coolant is a definitive sign.

Parts involved: Head gasket.

What it costs to put right

≈A$1,660 to ≈A$4,140 at independent workshop rates, shown as an approximate guide in Australian dollars. That is for this job on its own, not for the car.

An estimate, converted to Australian dollars, 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.

Ask the seller

“Have the head gaskets been replaced, and at what mileage?”
“Has the engine ever overheated?”
“Is there a full cooling system service history?”
“Has the car ever run low on coolant?”

Now check the Subaru STI you are actually looking at

Everything above is true of the model, and it is free. What it does not tell you is whether THIS car still has money owing on it, has been written off or reported stolen, what kms it showed in past sale ads, whether it has had accident repair claims and what it is worth today. That comes from the official records for that plate. Enter the plate and its state for the A$17.90 Vehicle Check, or the full history from A$24.99.

Where this comes from

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.

Subaru STI buyer questions

Is ej20/ej25 head gasket failure serious on a Subaru STI?

We rate it major and common on the Subaru STI. The EJ-series engines use a multi-layer steel (MLS) head gasket that seals between the aluminium cylinder head and the iron or aluminium block. Thermal cycling between the two dissimilar metals causes differential expansion rates that progressively fatigue the gasket fire-ring. On turbocharged applications, elevated coolant temperatures from heat soak, stuck thermostats, or coolant system neglect accelerate this failure. EJ25 engines (2.5 litre, used in the WRX from 2006 and in later STI models) are reported as more prone than EJ20 units because the larger bore leaves less metal between cylinders. Failure modes include external coolant leaks at the block-head joint, internal coolant-to-oil mixing, and combustion gas leaks that cause coolant system pressurisation. Many examples have had head gaskets replaced once already by 150,000 km.

How much does it cost to fix on a Subaru STI?

≈A$1,660 to ≈A$4,140 at independent workshop rates, shown as an approximate guide in Australian dollars. That figure is for this job on its own. A car showing the symptoms on this page is usually worth either walking away from or negotiating down by at least the repair figure.

Which Subaru STI years are affected?

Our research records this fault on the 2001–2014 Subaru STI. Build dates move around, especially on imported cars, so treat the range as the years to look hardest at rather than a guarantee either way. The official records tell you the exact build and first registration date for the car in front of you.