Subaru FB (1.6–2.5)

flat-4 · petrol · 2010–present

Also known as: fb20, fb25, 2.0 boxer, 2.5 boxer, fb engine, fb25b, fb16, fb25d

Subaru's current naturally aspirated flat-four — the boxer engine of the Impreza, Forester, Outback, Legacy and Crosstrek, replacing the long-running EJ family with a longer-stroke design and chain drive instead of a belt.

The horizontally opposed layout is the diagnostic frame for everything. Head gaskets are the fault the family is famous for, and while the FB improved substantially on the EJ's record, the geometry means a leak often appears as an external oil weep at the side of the engine rather than as coolant in the oil. The other consequence is access: spark plugs sit in the sides of the engine bay and are a substantially bigger job than on an inline four.

The FB's own recurring item is oil consumption on a defined range of early 2011–2014 engines, traced to piston rings and the subject of a service campaign. On an affected car a consumption complaint has a documented history behind it rather than being a wear finding.

It is a family spanning 1.6 to 2.5 litres — FB16, FB20 and FB25 — and the cars listed below carry all three. The oil-consumption campaign is dated rather than general, so it is a build-date question on a 2.0 or 2.5 and not a property of every FB.

Cars fitted with this engine

16 generations, across 1 make. From the authored catalogue — an absent car means the catalogue has not reached it, not that the engine was never fitted.

Subaru

Information, not instruction

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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.

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The car — make, model, year and engine. The same fault behaves differently on each.
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What actually fixed it — or that nothing did, which is worth knowing too.