The Subaru EJ204 is a 1,994 cc, flat-four naturally aspirated petrol engine produced between 1999 and 2006. It features dual overhead camshafts (DOHC), 16-valve configuration, and Subaru's Dual VVT system with multi-point fuel injection. In standard tune, it delivered 110 kW (150 PS) at 6,000 rpm and 183 Nm of torque at 3,600 rpm, offering balanced performance and refinement for everyday applications.
Fitted to models including the Legacy and Japanese-market Forester, the EJ204 was engineered for responsive driving dynamics and elevated fuel economy. Emissions compliance was achieved through close-coupled three-way catalytic converters and closed-loop lambda control, meeting Euro 3 standards across its production run.
One documented reliability concern is premature head gasket degradation, which could lead to coolant leaks, overheating, or engine misfires. This issue, highlighted in Subaru Service Information Bulletin SIB-EJ-021, is attributed to thermal stress and age-related sealing material fatigue. In 2003, Subaru introduced an upgraded MLS (multi-layer steel) head gasket with improved sealing layers and revised torque specifications to reduce failures.
Production years 1999–2006 meet Euro 3 emissions standards (VCA UK Type Approval #VCA/EMS/4037).
The Subaru EJ204 is a 1,994 cc flat-four naturally aspirated petrol engine engineered for mid-size applications (1999–2006). It combines DOHC valvetrain with sequential fuel injection to deliver smooth power delivery and improved drivability. Designed to meet Euro 3 standards, it balances daily usability with mechanical simplicity.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,994 cc | |
| Fuel type | Petrol | |
| Configuration | Flat-4, DOHC, 16-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 92.0 mm × 75.0 mm | |
| Power output | 110 kW (150 PS) @ 6,000 rpm | |
| Torque | 183 Nm @ 3,600 rpm | |
| Fuel system | Sequential multi-port fuel injection | |
| Emissions standard | Euro 3 | |
| Compression ratio | 10.0:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Double-row roller chain (DOHC) | |
| Oil type | Subaru 5W-30 (API SL) | |
| Dry weight | 132 kg |
The naturally aspirated flat-four provides smooth, linear power ideal for relaxed cruising but requires strict adherence to 15,000 km oil change intervals to prevent valvetrain degradation. Subaru 5W-30 oil is critical due to its formulation supporting hydraulic lifters and chain tensioners. Extended idling and short trips increase carbon buildup and oil contamination, accelerating head gasket wear. The 2003 update with MLS head gasket significantly improved durability; pre-2003 engines should verify head condition and consider preventative upgrades per Subaru SIB SIB-EJ-021.
Oil Specs: Requires Subaru 5W-30 specification (Subaru SIB SIB-EJ-021). Supersedes ACEA A3/B3 requirements.
Emissions: Euro 3 certification applies to all EJ204 models (1999–2006) (VCA Type Approval #VCA/EMS/4037).
Power Ratings: Measured under SAE J1349 standards. Output consistent across EU fuel grades (RON 95–98).
Subaru Technical Information System (TIS): Docs A29500, A29501, A29502, SIB SIB-EJ-021
VCA Type Approval Database (VCA/EMS/4037)
SAE International: J1349 Engine Power Measurement Standard
The Subaru EJ204 was used across Subaru's Legacy/Forester platforms with longitudinal mounting and no licensed external applications. This engine received platform-specific adaptations-higher-flow cooling in the Legacy and revised intake manifolds in the Forester-and from 2003 the updated MLS head gasket with improved sealing layers, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped on the front passenger side of the engine block near the cylinder head (Subaru TIS A29500). The 8th VIN digit indicates engine family ('E' for EJ series). Pre-2003 models have silver valve covers with black plastic timing covers; post-2003 units use black valve covers. Critical differentiation from EJ205: EJ204 uses a naturally aspirated 2.0L flat-four, while EJ205 is a turbocharged 2.0L flat-four petrol. Service parts require production date verification - head gaskets before 09/2003 are incompatible with later revisions due to internal redesign (Subaru SIB SIB-EJ-021).
The EJ204's primary reliability risk is head gasket failure on early builds, with elevated incidence in vehicles with extended service intervals. Internal Subaru quality reports from 2005 indicated a significant number of pre-2003 units required gasket replacement before 100,000 km, while UK DVSA records show coolant-related faults as a top cause of drivability complaints in Subaru petrol models. Extended service intervals and aggressive driving increase thermal stress, making coolant quality and schedule adherence critical.
Analysis derived from Subaru technical bulletins (1999–2006) and UK DVSA failure statistics (2000–2006). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about SUBARU EJ204.
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DVLA: Engine Changes & MoT
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Regulation (EC) No 715/2007
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Commission Regulation (EU) 2017/1151
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