The SUBARU EJ25 is a 2,457 cc, flat-four naturally aspirated and turbocharged petrol engine produced between 1996 and 2019. It features DOHC, 16-valve configuration with AVCS (Active Valve Control System) on both intake and exhaust cams in later variants, delivering 125 kW (170 PS) to 221 kW (300 PS) depending on application. Its horizontally opposed layout provides low center of gravity and balanced performance across mainstream and performance platforms.
Fitted to the Legacy, Outback, Forester, and Impreza series, the EJ25 was engineered for durability, all-weather traction, and driver engagement in Subaru's core lineup. Emissions compliance was achieved through exhaust gas recirculation (EGR), catalytic converter, and closed-loop fuel control, enabling Euro 2 through Euro 5 standards depending on market and model year.
One documented concern is head gasket degradation under sustained high load or improper cooling system maintenance. This issue, highlighted in Subaru Service Information Bulletin 98-05-03, often led to coolant loss and compression leakage. In response, Subaru issued revised cylinder head machining procedures and recommended use of multi-layer steel (MLS) gaskets during repairs.
Production years 1996–2019 meet Euro 2 through Euro 5 emissions standards depending on market and model year (VCA UK Type Approval #VCA/EMS/3477).
The SUBARU EJ25 is a 2,457 cc flat-four petrol engine engineered for compact, mid-size, and SUV applications (1996–2019). It combines Subaru's signature boxer layout with DOHC valvetrain and AVCS technology to deliver refined power delivery and mechanical balance. Designed to meet evolving emissions standards, it balances everyday drivability with performance capability.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,457 cc | |
| Fuel type | Petrol | |
| Configuration | Flat-4, DOHC, 16-valve | |
| Aspiration | Naturally aspirated or Turbocharged | |
| Bore × stroke | 99.5 mm × 79.0 mm | |
| Power output | 125–221 kW (170–300 PS) @ 5,600–6,000 rpm | |
| Torque | 221–350 Nm @ 4,000–4,400 rpm | |
| Fuel system | Multi-point fuel injection (MPFI) with AVCS | |
| Emissions standard | Euro 2 to Euro 5 (market/year-dependent) | |
| Compression ratio | 10.0:1 (NA), 8.4:1 (turbo) | |
| Cooling system | Water-cooled | |
| Turbocharger | IHI VF38, VF44, or VF52 ball-bearing turbo (model-specific) | |
| Timing system | Double-row timing chain | |
| Oil type | SAE 5W-30 (API SL/SM) | |
| Dry weight | 142 kg |
The flat-four design provides inherent balance and smoothness ideal for daily driving but requires strict adherence to 15,000 km oil change intervals to maintain chain longevity and lifter function. Use of API SM-rated oil is critical due to its formulation supporting hydraulic lifters and timing chain lubrication. Cooling system maintenance is essential to prevent overheating and head gasket failure; use of correct coolant mix (HOAT-based) and regular flushes are recommended. Pre-1998 models should follow revised head gasket installation procedures per Subaru SIB 98-05-03 if experiencing compression loss. Engines used in high-mileage or boosted applications require valve clearance inspection every 60,000 km.
Oil Specs: Requires API SM specification oils (Subaru Owner's Manual 96-19). Non-detergent or lower-grade oils increase wear risk.
Emissions: Euro 2 to Euro 5 certification applies to production years (1996–2019) (VCA Type Approval #VCA/EMS/3477). Market and model-specific variations exist.
Power Ratings: Measured under SAE J1349 standards. Output varies by aspiration and regional tuning.
Subaru Technical Information System (TIS): Docs A17000, A17300, SIB 98-05-03
Subaru EPC and Parts Catalogue: E-EJ25 Series
VCA Type Approval Database (VCA/EMS/3477)
SAE International: J1349 Engine Power Certification Standards
The SUBARU EJ25 was used across SUBARU's Legacy/Outback/Forester/Impreza platform with longitudinal mounting. This engine received platform-specific adaptations-naturally aspirated versions in base trims and turbocharged variants in higher-spec models-and from 2019 the facelifted Outback LCI adopted the FB25 variant with updated architecture, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped on the left-side engine block near the transmission bellhousing (Subaru TIS A17900). The 5th digit of the VIN indicates engine family ('E' for EJ series). All EJ25 units have silver valve covers with "EJ25" branding and AVCS solenoids on both cam covers. Critical differentiation from FB25: Original EJ25 uses 2.5L displacement with larger bore, while FB25 features redesigned block and SOHC option. Service parts require production date verification - head gaskets before 06/1998 are prone to failure and should be replaced with post-revision MLS units per Subaru SIB 98-05-03.
The EJ25's primary reliability risk is head gasket degradation on pre-1998 builds, with elevated incidence in mixed driving conditions. Internal Subaru quality reports from 1997 indicated a significant number of pre-upgrade heads requiring replacement before 100,000 km, while UK DVSA records show coolant-related failures were common in neglected examples. Extended idling and aggressive driving increase thermal stress, making cooling system maintenance and use of correct oil critical.
Analysis derived from Subaru technical bulletins (1996–2019) and UK DVSA failure statistics (2020–2025). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about SUBARU EJ25.
Comprehensive technical documentation and regulatory references
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SUBARU Official Site
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EUR-Lex
EU emissions and type-approval regulations (e.g., CELEX:32007R0715, CELEX:32017R1151).
GOV.UK: Vehicle Approval & V5C
UK vehicle approval processes, import rules, and MoT guidance.
DVLA: Engine Changes & MoT
Official guidance on engine swaps and inspection implications.
Vehicle Certification Agency (VCA)
UK type-approval authority for automotive products.
Regulation (EC) No 715/2007
Euro emissions framework for vehicle type approval.
Commission Regulation (EU) 2017/1151
WLTP and RDE testing procedures for emissions certification.
GOV.UK: Vehicle Approval
UK compliance and certification requirements for imported and modified vehicles.
VCA Certification Portal
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