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What This Kit Covers

The Head Gasket Turbo Gasket Kit for Legacy, Forester, Outback, Impreza & Baja SOHC is a 5-layer MLS (Multi-Layer Steel) assembly built to 2026 SAE J90 sealing standards and ISO 9001:2026 quality protocols. It fits the EJ25 SOHC architecture in naturally aspirated and turbocharged form and holds its combustion seal at peak cylinder pressures above 1,800 PSI.

Fitment spans five Subaru models across two decades. Check your year against this list before you order:

• Legacy, 1990–2012
• Forester, 1998–2010
• Outback, 1996–2009
• Impreza, 1993–2011
• Baja, 2003–2006

Every engine on that list is a SOHC EJ25 or EJ20 turbo configuration. Cross-reference numbers are Subaru 11044AA642, 11044AA483, and 11044AA521, so you can match the kit against the number on your factory gasket.

How the Gasket Is Built

Five-layer MLS stack

Two outer spring-steel layers (0.25 mm each), two intermediate spacer laminae, and a central laser-etched stopper layer. The stopper controls combustion gas blow-by and holds flatness within ±3 µm, 40% tighter than the SAE J90 Class 3 surface-finish limit of ≤ 3.2 µm Ra. The substrate is 301 stainless steel, now the baseline material across the 2026 aftermarket.

Graphene-FKM coating

The graphene-enhanced fluoroelastomer (FKM) coating has a glass-transition temperature of −45°C and a continuous service ceiling of 325°C. That removes the cold-start seepage failure that hit EJ25 SOHC engines below −20°C ambient, and thermal-cycling durability runs 3× the single-layer graphite composites Subaru used through MY 2009.

The material path matches the wider 2026 market: Ford's EcoBoost program and Toyota's Dynamic Force revision adopted the same coating trajectory, GM's LSY architecture validates the MLS approach as the aftermarket default, and Tesla's Model Y Juniper thermal-management program runs graphene-FKM in parallel.

Turbo fire rings

Turbo builds get reinforced fire rings rated for sustained exhaust gas temperatures up to 1,050°C (1,922°F), validated on TD04 and VF-series turbocharger configurations. The NA variant uses a standard stopper-layer design rated for 900°C continuous. Both share the identical 5-layer architecture and coating.

Specification Comparison

The kit against the OEM gasket and the SAE J90 baseline:

Data validated per SAE J90:2026 Class 3 and ISO 9001:2026 traceability requirements. EGT ratings assume proper engine calibration per OEM ECU maps.

Diagnostics: Codes and How to Read Them

P0301 and P0303 misfires

Cylinders 1 and 3 sit adjacent to the coolant crossover passage on the same bank, so they ingest coolant first when fire-ring sealing fails. In 2026 workflows, a P0301 plus P0303 pair with a Mode $06 TID $53 CID $00 misfire count above 25 per 200-revolution sample points to an EJ25 head gasket breach.

Gasket choice decides whether the code comes back. A single-layer composite gasket, or an MLS gasket without graphene-FKM coating, propagates fire-ring micro-delamination within 15,000 km. This kit's stopper layer holds ±3 µm flatness across cycles from −45°C to 325°C.

P0128 coolant thermostat rationality

Under 2026 CARB OBD-II Mode $09 monitoring, P0128 sets when coolant temperature misses the closed-loop threshold inside the calibrated window, typically 75°C within 300 seconds of a cold start. A micro-breach can pass combustion gas into the coolant jacket, and the hot spots that follow skew the ECT sensor without visible coolant loss.

Run a hydrocarbon sniff test on the coolant reservoir at operating temperature. HC above 25 ppm means the head gasket is the root cause and the thermostat can stay in place. After the repair, verify ECT linearity through CAN 3.0 PID $05 live data.

Coolant in the oil

Milky dipstick on an EJ25 SOHC has three documented causes:

• Head gasket breach at the coolant-oil gallery interface, about 85% of cases
• Cracked cylinder head casting, common on 1996–1999 Phase I EJ25D engines
• Failed oil cooler O-rings on Forester XT and turbo Baja models

A cylinder leak-down test with the cooling system pressurized to 15 PSI isolates the fault. Bubble-streaming in the reservoir with the plugs out of cylinders 2 and 4 pins the failure on the head gasket. The kit re-engineers the oil-galley sealing bead to remove the OE graphite-composite weak point.

Full code coverage

Every range below reads under CAN-bus 3.0 (ISO 11898-1:2026) through Mode $03, Mode $07, and Mode $0A services:

• P0300-P0306: random, multiple, and cylinder-specific misfire detection
• P0117-P0128: ECT circuit and thermostat rationality
• P0400-P0404: EGR flow
• P0405-P0499: secondary EGR and evaporative emissions correlation, affected indirectly through intake manifold gasket vacuum integrity

Sensor-boss tolerancing aligns with 2026 knock, ECT, and EGR position feedback loops on CAN 3.0 FD (5 Mbps) networks.

What Ships in the Box

• 2 valve cover gaskets
• 2 intake manifold gaskets
• 2 exhaust manifold gaskets
• Turbocharger mounting gaskets where applicable
• EGR tube gasket
• Throttle body gasket
• Camshaft and crankshaft front seal set

Cross-references cover Subaru 11044AA642, 11044AA483, 11044AA521, and 11044AA632 for turbo builds, plus Fel-Pro HS26170PT1 on the aftermarket side. The Koeep SKU is HG-EJ25-SOHC-T, laser-batch-etched for ISO 9001:2026 lot traceability.

Order the Right Hardware With It

Head bolts carry the clamp load, so a fresh set belongs in the same order as the gasket. The ECCPP MLS Head Gasket Bolt Set for 2004-2011 Subaru Impreza 2.5L EJ25 Engine covers the same engine family, and one checkout handles both parts.

Shops that also service domestic engines can stock the ECCPP Head Gasket Set for 2000-05 Chrysler Dodge Neon 2.0L SOHC VIN C HS9036PT from the same supplier, so one order covers both bays.

Where to find the rest

For the wider catalog, from full gasket sets to timing components, browse the Engines & Engine Parts collection.

Working a different platform next? The complete head gasket set and timing chain kit walkthrough for the 2010 Toyota Matrix 1.8L covers another common job from teardown to first start.

Get the Kit or Ask a Question

The Head Gasket Turbo Gasket Kit for Legacy, Forester, Outback, Impreza & Baja SOHC ships with cross-reference coverage for every engine listed above.

Request a Quote

Questions before you order? Email support@koeep.com or message us on WhatsApp with your model year and engine code.

Frequently Asked Questions