The Subaru FB25 is a 2,498 cc, flat-four petrol engine produced between 2011 and 2021. It features a DOHC 16-valve configuration with Dual AVCS (Active Valve Control System), port fuel injection, and Atkinson cycle operation, delivering 131 kW (178 PS) in standard applications. Part of Subaru's FB series designed for improved efficiency and reduced friction, it was engineered to balance fuel economy with smooth power delivery across mid-size platforms.
Fitted to models such as the Outback (BM/BT) and Legacy (BM/BT), the FB25 was designed for drivers seeking reliable everyday performance with Subaru’s signature AWD capability. Emissions compliance was achieved through exhaust gas recirculation (EGR), close-coupled catalytic converters, and oxygen sensor feedback control, enabling it to meet U.S. EPA Tier 2 Bin 5 standards across its production run.
One documented reliability concern is timing chain guide wear under prolonged high-RPM operation, highlighted in Subaru Service Information Bulletin SSB-12-027. This issue is often associated with extended oil change intervals or use of non-specified lubricants. In 2014, Subaru revised the tensioner design and introduced updated polymer guides to improve durability.
Production years 2011–2021 meet U.S. EPA Tier 2 Bin 5 standards; Canadian and European variants comply with equivalent national regulations (VCA UK Type Approval #VCA/EMS/2315).
The Subaru FB25 is a 2,498 cc flat-four naturally aspirated engine engineered for mid-size applications (2011–2021). It combines Subaru's horizontally-opposed layout with Dual AVCS and Atkinson cycle operation to deliver responsive torque and ultra-low fuel consumption. Designed to meet Tier 2 Bin 5 emissions, it balances city drivability with environmental compliance.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,498 cc | |
| Fuel type | Petrol | |
| Configuration | Flat-4, DOHC, 16-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 94.0 mm × 90.0 mm | |
| Power output | 131 kW (178 PS) @ 5,800 rpm | |
| Torque | 235 Nm @ 4,100 rpm | |
| Fuel system | Multi-point fuel injection (MPI) | |
| Emissions standard | U.S. EPA Tier 2 Bin 5 | |
| Compression ratio | 10.0:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Chain-driven (front-mounted) | |
| Oil type | SAE 0W-20 (API SN) | |
| Dry weight | 142 kg |
The Atkinson cycle flat-four layout provides exceptional fuel economy ideal for urban driving but requires adherence to maintenance schedules to sustain longevity. SAE 0W-20 oil meeting API SN specifications is recommended for optimal lifter and camshaft lubrication. Oil changes should occur every 15,000 km or annually to prevent sludge buildup and timing chain wear. The interference design means valve damage will occur if the timing system fails. Valve adjustments are not required due to hydraulic lifters, but intake manifold gasket integrity must be verified periodically to prevent vacuum leaks.
Oil Specs: Requires API SN-rated 0W-20 oil (Subaru SIB SSB-12-027). Compatible with ILSAC GF-5 requirements.
Emissions: Tier 2 Bin 5 certification applies to all production years (VCA Type Approval #VCA/EMS/2315). No Euro 5-equivalent variants were produced.
Power Ratings: Measured under JIS D 1001 standards. Output achieved with 91 RON fuel and optimal ignition timing (Subaru TIS Doc. A25PERF).
Subaru Technical Information System (TIS): Docs A25FB, A25FUEL, A25TIMING
VCA Type Approval Database (VCA/EMS/2315)
JIS D 1001: Internal combustion engine — Test code
The Subaru FB25 was used across Subaru's Outback and Legacy platforms with longitudinal mounting and symmetrical all-wheel drive. This engine received platform-specific adaptations-reinforced mounts in the Outback BM/BT and revised intake manifolds in the Legacy BM/BT-and from 2014 the updated Outback III Facelift models adopted revised piston rings and oil squirters, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped horizontally on the front-left cylinder block near the exhaust manifold (Subaru TIS A25ID01). The 4th digit of the VIN indicates engine family ('F' for FB series). Pre-2014 models have silver valve covers with ribbed rocker housings; post-2014 units use black valve covers with revised fastener layouts. Critical differentiation from EZ36D: FB25 has smaller displacement and different crankshaft. Service parts require production date verification - timing chain kits for pre-2014 models are incompatible with later revisions due to internal cooling passage updates (Subaru SIB SSB-12-027).
The FB25's primary reliability risk is timing chain guide degradation on high-mileage engines, with elevated incidence in vehicles subjected to sustained highway operation. Internal Subaru engineering reports noted increased guide fracture rates beyond 150,000 km, while UK DVSA field data shows a notable share of noise-related MOT failures linked to chain rattle. Extended high-speed driving and delayed maintenance increase thermal stress, making oil quality and flush intervals critical.
Analysis derived from Subaru technical bulletins (2011-2021) and UK DVSA failure statistics (1995-2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about SUBARU FB25.
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