Subaru Engine Guides — EJ, FA, FB & EZ Boxer Deep Dives

Subaru has built five distinct families of horizontally-opposed 'boxer' engines for the US market — EJ, EZ, FA, FB, and the current FA24 turbo — and each one has a personality, a service ceiling, and a short list of failures that separate a good used example from an expensive lesson. This hub is where we collect every engine-specific teardown, cost breakdown, and buying-guide caveat we've written so you can walk into a used-Subaru sale knowing what the seller isn't telling you.

The EJ25 SOHC that lived under Outbacks, Legacys, Foresters, and base Imprezas from 1999 through 2012 is the reason 'Subaru head gasket' is a meme. The failure is external, between the cylinder and the oil gallery, and Subaru's own 6-layer 11044AA770 gasket is the permanent fix — but only if the shop resurfaces the heads and torques the new TTY bolts correctly. Bundle it with the timing belt and you save four hours of duplicate labor.

The FA20DIT that turbocharged the VA WRX from 2015–2021 is a different beast. Ringlands crack on lean cylinders under boost, rod bearings spin when owners run the wrong oil weight or extend intervals past 3,750 miles, and the RTV pickup-tube fiasco has scrapped more short-blocks than any single Subaru defect since the EJ head gasket. The FA24 that replaced it in the VB WRX solved the ringland issue but introduced its own PCV, oil-cooler, and CVT-integration problems we're still cataloging.

On the naturally-aspirated side, the FB25 in modern Foresters, Outbacks, and Ascents has an oil-consumption story that mirrors the EJ25's head-gasket story: Subaru acknowledged it, extended warranties on a subset of VINs, and updated the piston rings mid-generation. Whether the fix reached your specific serial number is the question our FB25 guide answers.

And then there are the enthusiast engines — the EJ257 STI closed-deck, the FA20 in the BRZ/86 with its valve-spring recall, the EZ36 flat-six in the 3.6R Outback and Tribeca — each with a small but loyal audience and a very specific list of things that go wrong past 120,000 miles.

Use the cards below to jump to the engine family in your car, the repair-cost breakdowns we've priced against dealer, indy, and DIY, and the model-specific hubs where all of this ties back to the buying-guide recommendations.

Oil choice is where most Subaru engine failures start. The FA20DIT and FA24DIT both call for 5W-30 API SN Plus or SP with a low-SAPS additive package — running 5W-40 to 'protect' the engine actually starves the variable-cam solenoids and accelerates timing-chain guide wear. The FB25 wants 0W-20 dexos-approved oil at a strict 6,000-mile interval on the post-2019 revision; the pre-2019 short-blocks need 5,000 miles or the piston-ring oil-consumption spiral starts. The EJ25 SOHC is the outlier — it doesn't care about weight nearly as much as it cares about being changed. 3,000-mile intervals on inexpensive conventional oil outperform 7,500-mile intervals on premium synthetic in almost every long-term data set we've seen from Subaru specialists.

Every Subaru boxer has a service ceiling — the mileage past which preventive-work cost exceeds the depreciation curve of the car. On the EJ25 SOHC it's roughly 180k with a fresh head-gasket job; past that, the second gasket failure becomes hard to defend economically. On the FA20DIT it's around 130k without a rebuild — ringlands, valve seats, and rod bearings all trend past their fatigue life around then. The FB25 in a modern Forester or Outback runs comfortably past 220k with fluid discipline. The EZ36 flat-six is the exception again: an overbuilt long-block that outlasts everything bolted to it, provided the chain guides are done by 130k. Those ceilings are what our year-by-year buying guides use to score used-car listings.

If you're diagnosing a specific noise, tick, or oil-consumption complaint, jump straight to the failure-guide cards below — each one lists the OBD-II codes to expect, the compression numbers a healthy example should return, and the specific dealer TSB or extended-warranty campaign that might apply. If you're shopping used, the comparison table above is the fastest way to check whether the engine in your target car has an active warranty extension or a known-fix service bulletin worth verifying before writing a check.