Subaru head gasket problems are most often reported on the naturally aspirated 2.5-liter EJ25 engines used in many Outback, Forester, Impreza and Legacy models of the 1990s and 2000s, which commonly leaked oil or coolant where the cylinder heads meet the block. On turbocharged EJ255 and EJ257 engines in the WRX and STI the more feared failure is ringland failure, a cracked piston usually caused by detonation. Both are repairable; the right fix depends on the damage and on how much power the engine will make.
Subaru head gasket symptoms
- Oil or coolant seeping from the joint between the cylinder heads and the block
- Coolant loss with no obvious leak, or a sweet coolant smell
- Overheating, especially under load or on hills
- Bubbles in the coolant reservoir or white exhaust smoke
Our signs of a blown head gasket guide explains how to test for a leak.
Fixing a Subaru head gasket
A head gasket job on a boxer engine usually means removing the engine. With the heads off, they are checked for flatness and resurfaced if needed, and new gaskets, usually multi-layer steel, are fitted with new head bolts or studs. Because so much labor is involved, owners often replace timing components and seals at the same time. Repair cost depends mostly on labor and on what else is found once the engine is apart, so get a written estimate before deciding.
Head gaskets on turbo EJ25 engines
The factory EJ25 block has an open deck: the cylinder tops are supported only at the ends. At high boost the cylinders can move, which makes the head gasket harder to seal. A closed deck block adds support around the cylinders, and head studs add clamping force; see closed deck vs open deck.
What is ringland failure?
The ring lands are the thin sections of the piston between the ring grooves. On the factory cast pistons in turbo EJ engines, detonation can crack a ring land, which lets compression escape past the rings. Detonation can come from low-octane fuel, a lean mixture, too much ignition advance or high intake temperatures.
Ringland failure symptoms
- Low compression on one cylinder in a compression or leak-down test
- A misfire on that cylinder; see engine misfire
- Rising oil consumption, smoke or crankcase pressure
A cracked piston cannot be repaired in place. The engine needs new pistons, which in practice means rebuilding the short block, and many owners choose forged pistons at that point.
Short blocks and long blocks we carry
We carry closed deck EJ25 short blocks and long blocks for the 2002-2014 WRX, 2004-2021 STI, 2004-2013 Forester XT and 2005-2009 Legacy GT from IAG Performance and Turn In Concepts. Many of the IAG builds list JE forged pistons and IAG’s head gasket sealing upgrades; each listing details its pistons, rods and gasket setup. Compare them on our EJ25 short blocks and long blocks page, read EJ255 vs EJ257, and see Subaru WRX and STI parts for clutches, exhausts and suspension.
More guides: Subaru timing belt · oil in coolant · EJ257 problems · Subaru boxer engine basics · EJ25 problems · FA20 problems · forged vs cast pistons · how long a Subaru engine lasts · head studs vs head bolts · Subaru oil pickup tube.
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