EJ25 Head Gaskets: Why They Fail and How to Keep Yours Alive

EJ25 head gaskets fail for two reasons: early non-turbo EJ25s used a gasket design that was prone to leaking, and any EJ25 will lift a gasket if it overheats. Which one you're fighting depends on your engine. The fix is the same for both: a healthy cooling system, and MLS gaskets if the heads ever come off.

Here's how to tell what you've got, what to watch for, and what to do about it.

Which EJ25s are most at risk

Not all EJ25s are equal. The head gasket reputation mostly belongs to the early non-turbo engines.

Early composite gaskets were prone to failure, and Phase II engines mainly leaked externally. Subaru's response in some markets was a cooling system conditioner and extended warranty, not a redesigned part. Turbo engines run multi-layer steel (MLS) gaskets and fail less often, but higher-boost tunes raise the risk. (Source: SlashGear, citing MartiniWorks)

Turbo EJs have one more weak spot. Coolant flow around cylinder 4 is uneven, so it runs hotter than the others. That hot spot raises knock risk on tuned and tracked cars, which is why the Cylinder Four Cooling Mod exists.

Warning signs

Catch it early and it's a gasket job. Ignore it and it's warped heads or a full rebuild.

External leak (common on Phase II)

• Oil or coolant weeping where the heads meet the block
• A sweet coolant smell after a drive
• Coolant level slowly dropping, crusty residue on the block

Internal leak (more serious)

• Bubbles in the overflow tank when the engine is warm
• White exhaust smoke that doesn't clear once warm
• The temperature gauge climbing under load or on hills
• Milky residue under the oil cap
• Coolant disappearing with no visible leak

If you see the internal signs, stop driving it hard and get a combustion leak test (block test). It checks the coolant for exhaust gas, it's cheap, and it gives you a clear answer before you spend real money.

How to prevent it

Most of this is basic cooling system care. Overheating is what turns a weak gasket into a failed one.

1. Service the coolant on schedule. Use the coolant your car specifies and don't mix types. Older EJs on conventional coolant typically need it every two years.
2. Bleed the system properly. Air pockets in a boxer engine create hot spots in the heads, exactly where gaskets fail. Bleed it every time the system is opened.
3. Replace the thermostat and hoses before they fail. A sticking thermostat or a burst hose can overheat an engine in minutes. Rubber hoses on 15- to 25-year-old cars are overdue. See our Genuine Ancillary Coolant Hose Sets and silicone hose kits.
4. Fit a fresh radiator cap. A tired cap can't hold pressure, so coolant boils sooner. The Fuji Racing 1.3 bar cap fits most Subarus.
5. Never drive through overheating. If the gauge climbs, pull over. One serious overheat can warp a head.
6. On a tuned turbo EJ, address the hot spot. The Cylinder Four Cooling Mod evens out coolant flow, and a sensible tune matters more than peak boost.

If the gasket has already gone

The heads come off both sides of the engine, so do the job once and do it properly:

• Have both heads checked for flatness and machined if needed
• Fit MLS head gaskets. We stock EJ25 MLS gaskets in 0.8mm, 1.1mm and 1.5mm. Thickness changes compression, so match it to your build.
• On turbo engines, fit head studs instead of reusing the factory bolts. We stock 11mm and 14mm kits; which one suits depends on your engine.
• Replace the thermostat, water pump and timing components while you're in there, then refill and bleed carefully.

Not sure which gasket thickness or stud kit you need? Send us your VIN and build details through the Parts Enquiry page.

EJ25 head gasket FAQs

Why do Subaru EJ25 head gaskets fail?

Early non-turbo EJ25s (about 1996–2004) used a gasket design prone to leaking. Any EJ25 will also lift a gasket after overheating, usually from neglected coolant, air in the system or a failed hose or thermostat.

Which Subaru engines have head gasket problems?

Mainly Phase I and Phase II non-turbo EJ25s fitted to the Liberty, Outback, Forester and Impreza RS. Turbo EJ255 and EJ257 engines use MLS gaskets and fail less often, mostly after overheating or with aggressive tunes.

What are the signs of a blown head gasket on an EJ25?

External: oil or coolant weeping at the head-to-block joint. Internal: bubbles in the coolant tank, white smoke, overheating, milky oil or coolant loss with no visible leak.

Can you prevent EJ25 head gasket failure?

You can greatly reduce the risk. Keep the coolant fresh and properly bled, replace the thermostat, hoses and radiator cap before they fail, and never drive an overheating engine.

Should I use MLS head gaskets on an EJ25?

Yes. If the heads are coming off, multi-layer steel gaskets are the standard upgrade, paired with head studs on turbo engines.

The Roo Racing take

The EJ25's head gasket reputation is earned, but it isn't a death sentence. Early engines got a weak gasket, and every EJ punishes overheating. Look after the cooling system and most EJ25s will never need the job. If yours does, do it once with MLS gaskets, flat heads and proper studs, and it'll outlast the factory setup.

Further reading

• EJ Turbo Reliability Starts With Maintenance: 5 Checks That Actually Matter
• EJ vs FA: What Changed Between Subaru's Two Turbo Platforms
• 5 Common Problems with Subaru's Turbocharged EJ Platform