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.
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Production years 2011–2021 meet U.S. EPA Tier 2 Bin 5 standards; Canadian and European variants comply with equivalent national regulations .
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 | Refer to vehicle handbook / manufacturer specification | |
Dry weight | 142 kg |
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.
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Field reports and technical service bulletins highlight component wear patterns under high-load operation. Adherence to manufacturer service intervals and approved fluid specifications is critical for long-term reliability.
Analysis derived from manufacturer technical service bulletins and industry workshop records. Repair procedures should follow manufacturer guidelines.
The most common questions about engine codes, what they mean, how to find them and how this database works
The FB25 is a robust, low-stress engine when maintained properly. Regular oil changes (every 15,000 km) and coolant flushes (every 2 years) are essential. Engines with documented service history and no overheating incidents can exceed 250,000 km reliably. Its DOHC design and conservative tuning contribute to long-term durability in daily driving applications.
The most common issues include timing chain guide wear, ignition coil failure, throttle body carbon buildup, and valve cover oil leaks. These are documented in Subaru service literature and prevalent in high-mileage or poorly maintained examples. Preventative maintenance significantly reduces failure risk.
The FB25 was used in the Subaru Outback (BM/BT, 2011-2021) and Legacy (BM/BT, 2011-2021). It was available in both FWD and AWD configurations depending on market. The engine was phased out in favor of the FA24 turbocharged four-cylinder in later model years.
Aftermarket ECU tuning is common on the FB25 platform, but increasing boost or altering engine parameters accelerates component wear, impacts emissions compliance, and may void vehicle warranties. Any modifications should be evaluated carefully by a qualified specialist.
Fuel consumption is excellent for its class. In the Outback 2.5i, combined consumption is approximately 7.8 L/100km (~36 mpg UK). City driving may exceed 9.2 L/100km (~31 mpg), while highway cruising can achieve ~6.6 L/100km (~43 mpg). Driving style significantly impacts real-world economy.
Yes. The FB25 is an interference engine. If the timing chain fails or skips, the pistons will contact the valves, resulting in severe internal damage. The front-mounted chain is durable but must be inspected regularly, especially in high-heat climates.
Subaru specifies SAE 0W-20 oil meeting API SN standards. This viscosity is essential for lifter quietness and camshaft protection. Oil must be changed every 15,000 km or annually, and OEM-approved filters should be used to ensure proper flow and filtration.
Comprehensive technical documentation and regulatory references
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Regulatory Stability
EU regulations are referenced using CELEX identifiers for long-term stability.
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
Type-approval guidance and documentation.
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