FB25 Engine in Phoenix, Arizona
The engine that replaced the EJ25 in most naturally aspirated Subarus, designed from the ground up to fix the head gasket problems that defined the EJ era.
- Family
- FB25 (FB-series)
- Displacement
- 2.5 L
- Configuration
- Flat-four (boxer), 4-cylinder
- Valvetrain
- DOHC, 16 valves, AVCS
- Produced
- 2011 onward
Bore and stroke are omitted for this family: the code covers variants with different figures, and a single pair of numbers would be wrong for some of them.
The FB25 is a 2,498 cc flat-four that Subaru introduced for 2011 as the replacement for the EJ25 in naturally aspirated applications. It uses a timing chain rather than a belt, direct injection on later variants, and a redesigned block and head that address the head gasket problems that made the EJ25 notorious.
In Phoenix the FB25 matters because it is the engine in most 2011-and-later Foresters, Outbacks, Legacys and Crosstreks that are not turbocharged. These vehicles are numerous in the Valley, they are reaching the age where engine questions arise, and the FB25 is the engine that replaced the EJ25 the previous generation owners dealt with.
The critical buying point is that the FB25 is not interchangeable with the EJ25 despite the similar displacement and boxer layout. Different block, different heads, different timing drive, different accessories. An FB25 will not drop into a car that came with an EJ25.
Built to fix the EJ25's problem
The FB25 replaced the EJ25 not through a different gasket on the same block but through a redesigned block, different head gasket surfaces and a timing chain instead of a belt. It is a fundamentally different engine that happens to share a displacement and a boxer layout.
This is why the head gasket questions that dominate EJ25 buying do not apply to the FB25. The failure mode it was designed to address is a structural one, not a material one.
Not interchangeable with EJ25
The FB25 and EJ25 have different blocks, different heads, different timing drives (chain versus belt) and different engine management. An FB25 will not drop into a car that came with an EJ25 without substantial conversion work.
Forester, Outback, Legacy and Crosstrek applications share the FB25 family but differ in accessory layout and wiring. Supply year, trim and VIN.
Vehicles built with a FB25
Subaru Forester, Outback, Legacy and XV Crosstrek from 2011 onward, each with its own accessory and wiring configuration.
| Vehicle | Years | Trim / body | Engine code | Market |
|---|---|---|---|---|
| Subaru Forester | 2011–2018 | : | FB25 | USDM |
| Subaru Outback | 2013–2019 | : | FB25 | USDM |
| Subaru Legacy | 2013–2019 | : | FB25 | USDM |
| Subaru XV Crosstrek | 2013–2017 | : | FB25 | USDM |
FB25 variants
Two principal variants. The standard FB25 and the later FB25-AVCS with active valve control on both camshafts.
- FB25Both
- The standard 2.5-litre naturally aspirated specification across Forester, Outback, Legacy and Crosstrek.
- FB25-AVCSBoth
- Later variant with active valve control system on both intake and exhaust camshafts.
Identifying a FB25
- The FB25 and EJ25 are both 2.5-litre boxers but are different engines. The FB25 uses a timing chain; the EJ25 uses a timing belt. That is the quickest structural distinction.
- The FB25 block has a different casting from the EJ25, with different oil and coolant passages and a different head gasket surface.
- The AVCS system on the FB25 operates differently from the variable valve timing on the EJ25, and the wiring and solenoids are in different locations.
A seller describing an engine as a particular variant is making a checkable claim. Asking for a photograph of the stamp on the actual unit is not a sign of distrust; it is the normal way this gets confirmed. The engine code guide shows where each family is stamped if you want to read the one in your own car first.
What varies between FB25 units
These are the differences that decide whether two engines with the same family code are substitutes in a particular car.
- The FB25 is NOT interchangeable with the EJ25. Different block design, different accessories, different timing chain versus belt and different engine management.
- Forester, Outback, Legacy and Crosstrek applications share the FB25 family but differ in accessory layout and wiring. Supply the year, trim and VIN.
- The FB25 addressed the EJ25 head gasket problem through design changes, not through a different gasket material on the same block. This is a fundamentally different engine.
Nothing on this page confirms that a specific FB25 will work in your vehicle. That takes the year, model and trim at one end and a specific unit at the other, and it happens before a price is given rather than after. What goes into that check is set out here.
Ask about a FB25 for your vehicle
The code is pre-filled. Add the year, model and trim, and the variant question gets settled on our side before anything is confirmed.
Common questions
Is the FB25 better than the EJ25?
The FB25 addressed the head gasket problems that were the EJ25's most common failure through a redesigned block, different head gasket surfaces and a timing chain instead of a belt. It is a more modern engine with different maintenance requirements. Whether it is "better" depends on what you mean, but the head gasket question that dominates EJ25 buying does not apply to the FB25.
Can I replace my EJ25 with an FB25?
No. Despite the similar displacement and boxer layout, the FB25 and EJ25 are different engines with different blocks, heads, timing drives and engine management. An FB25 will not drop into a car that came with an EJ25 without substantial conversion work that is not practical as a replacement.
Related pages
- EJ25 EngineSubaru’s 2.5 boxer, head gaskets included.
- EJ20 EngineThe 2.0 Subaru boxer from the JDM WRX and STI.
- FA20 EngineSubaru's modern 2.0 boxer, co-developed with Toyota for the BRZ.
- Subaru ForesterEJ25 head gaskets, and whether to repair or replace.
- Subaru EnginesSubaru boxer engines, head gaskets, and what replacement involves.
- What Comes With a JDM EngineWhat is usually attached, what almost never is, and what to confirm in writing.
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