So you’re interested in buying a Subaru. Maybe you want to stand out in a sea of same-looking commuter cars, or maybe you just appreciate the all-all-wheel-drive (BRZ aside) lineup. Either way, you’ve made an erudite choice. Before you buy, though, you should know about the single biggest Subaru uniquity: the company’s engines.
Subaru is one of two manufacturers to use flat engines in their cars (well, two and a couple halves, but we’ll get to that), and it’s the only car company that doesn’t build any other kind of engine. Even Porsche, maker of the flat-engined Boxster and 911, uses more traditional configurations in its crossover lineup.
This makes buying a Subaru an interesting proposition for the untrained. It’s a whole new world to deal with mechanically, and many buyers find themselves lost in forum threads, barely treading acronym-filled waters, trying to wrap their heads around a four-digit mechanic quote that just reads “head gaskets.” Luckily for you, we (with the help of the Subaru engine wizards at IAG) are here to help — breaking down every Subaru engine you’re likely to see for sale, and how to know if the one you’re looking at is healthy or hurting.
The EJ Series
Found in: *Deep breath in* 2002-2012 Subaru Impreza (including WRX and STi), 1998-2012 Subaru Legacy/Outback (including GT and XT), 2003-2006 Subaru Baja (including Turbo), 1998-2011 Subaru Forester (including XT), 2005-2006 Saab 9-2x (including Aero), 2012-2014 Subaru Impreza WRX, 2014-2021 Subaru WRX STI
When most people think of “a Subaru engine,” they’re thinking of this series. The EJ line powered every Subaru from the late ‘90s through to the early 2010s with various versions, displacements, and induction methods. Your Imprezas, Legacies, Foresters, even the Baja — all had an EJ-series engine under the hood.
The EJ-series engines are, admittedly, a bit of a tough sell in 2022. The line was first introduced in 1989, and while the updates it received through its thirty two years of service did their best to keep it competitive, there’s only so far that old engineering can go. EJs aren’t exactly known for their fuel economy, high-mileage reliability, or for keeping their oil inside the block but outside the combustion chamber — what we in the biz call “where the oil is supposed to go.”
While the EJ may not stand up to a modern Subaru engine for daily driving, however, enthusiasts will likely never let the line die. The performance aftermarket for these engines is staggering, and their decades of use mean parts and information are readily accessible. Want to know how a certain modification will affect your WRX? Forum posts dating back to the dot-com bubble will have your answer.
The question of “Should you buy an EJ-powered Subaru” is really one of personal choice. Would you rather have modern engineering and a (likely) lower-mileage engine with an FA or FB, or do you prefer the older platform where every kink and pitfall has been explored and documented? Are you concerned about the availability of parts for an engine that’s no longer used in production vehicles, or does thirty years of aftermarket support make up for what you’d miss at the dealer’s parts counter?
Since the EJ is no longer used by Subaru, the ones you see on the roads (or on Facebook Marketplace) today are all reaching that age where certain maintenance items are due, regardless of mileage. Primarily, that means timing belts — every 90,000 miles or six years, an EJ needs a timing belt change. If you’re looking at a Subaru with no record of that service, just have it done. The peace of mind is worth it.
The EJ engines are also the most distinctive sounding of the Subaru stable. That boxer burble we all know and love is due to the exhaust manifolds that came factory on these engines. The packaging constraints of that factory setup led to one side of the exhaust manifold being considerable longer than the other (they’re called, creatively, “unequal length”), and the difference in distances the exhaust pulses travel leads to that beloved rumble.
The First USDM WRX Engine: EJ205
Found in: 2002-2005 Subaru Impreza WRX, 2005 Saab 9-2x Aero
In 2002, Subaru’s world-renowned performance sedan finally hit American shores. The WRX was a weird, bug-eyed little four-door (or wagon) with a cheap interior and a transmission that would go all Infinity War if you looked at it wrong. Its engine, though, was a masterpiece for the time. You got two liters, 227 horsepower, and a burbling soundtrack for your daily commute.
Twenty years on, though, the early WRX’s EJ205 has revealed some imperfections. Watch for oil leaks from the valve cover or return line on the turbocharger, and coolant leaks from the expansion tank. The plastic-and-rubber hose that feeds air into the turbo will dry out and crack with age, and I can tell you from personal experience that it’s not a fun part to swap out by yourself.
Early EJ205s had an issue with fuel lines leaking on cold starts, but Subaru issued a Technical Service Bulletin to fix it. Check if that work’s been done before buying an ‘02 or ‘03. Also check the condition of the crank pulley, AC belt tensioner, and the nest of vacuum hoses that permeate the engine bay.
When modified or poorly maintained, EJ205s are susceptible to rod bearing failure. Listen for a tapping sound that varies with RPMs, though it may be too quiet to hear at low engine speeds. If you hear it, don’t buy the car — or start negotiating its price as a rolling shell.
It’s worth noting that these engines, when they fail, are often replaced with JDM EJ205 engines. The Japanese variant had a form of variable cam timing called AVCS that the U.S.-spec cars lacked, so be very careful if you find a WRX that’s had a new engine popped in. Without proper AVCS control, which the U.S. cars have no factory wiring for, the Japanese engine won’t run right.
The JDM Holy Grail STi Mill: EJ207
Found in: Never offered from Subaru in the U.S., but commonly swapped into WRXes and STis.
I know, I told you that this list would be a guide to the engines you’re likely to see when car shopping. How could a Japanese-spec engine, never sold by Subaru in the States, fit in here? Well, Subaru engines are known to fail, and when they do they leave a boxer-four-cylinder-shaped hole under the hood of a performance car. It’s become common practice for owners to swap in in the high-revving JDM engine of their dreams.
Most of the EJ205's issues crop up with the EJ207 too. Oil leaks, coolant leaks, air leaks, crank pulley failures, tensioner failures, rod bearing failures. Being another JDM engine, AVCS control issues are also worth looking out for.
Also be on the lookout for piston slap, since some versions of the EJ207 (the V6 and V7, specifically) came from Subaru with forged pistons. Forged parts need different tolerances, and a forged piston will chatter on cold starts — not to mention the excess oil consumption caused by your black gold blowing past the piston rings and into the combustion chamber. Still, these pistons are sought out for their strength, meaning you can hold more power on stock engine internals.
The Head-Gasket-Eating 2.5-Liter: EJ25D/EJ251/EJ253/EJ259
Found in: Base engine for the 2002-2012 Subaru Impreza, 1998-2012 Subaru Legacy/Outback, 2003-2006 Subaru Baja, 1998-2011 Subaru Forester, 2005-2006 Saab 9-2x
The naturally-aspirated commuter engines that served Subaru for over a decade. There are a few variants here, but they’re all relatively minor revisions of each other. (The outlier is the EJ25D’s dual overhead cam design, which makes it unique among the otherwise single overhead cam group.) When you hear about Subarus blowing their head gaskets, these are the engines in question. And, before you mention it — yes, the gaskets were revised late in the engine’s run, but they’re still known to fail on even the latest versions.
To sniff out head gasket failure, start by actually sniffing. If the tailpipe is pumping out sweet-smelling white clouds, you’ve got a problem on your hands. Check the coolant reservoir too for any bubbling or mixing of liquids, as well as looking underneath for signs of weeping where the block meets the heads. Remember that, despite being only four cylinders, EJ engines have two cylinder heads — the flat layout means you’ve got double the chance of failure, and (potentially) double the cost of repair.
Beyond the head gaskets, the other EJ warnings apply here. Timing belt issues, oil leaks, and rod bearing failures still happen on these naturally-aspirated models — though bearing issues are certainly less common here than on modified turbo engines.
You might be curious about the Saab listed above. For two glorious years, 2005 and 2006, General Motors (then-owner of Saab and stakeholder in Subaru) struck a weird deal with the six-starred manufacturer. The Subaru Impreza was rebadged and sold as the Saab 9-2X, with the WRX showing up as the Saab’s Aero trim. These are commonly called Saabarus, can only be found as station wagons, and are exceptionally cool.
The 2.5-Liter WRX Engine: EJ255
Found in: 2006-2014 Subaru Impreza WRX, 2004-2013 Subaru Forester XT, 2005-2012 Subaru Legacy GT, 2005-2009 Subaru Outback XT, 2004-2006 Subaru Baja Turbo, 2006 Saab 9-2x Aero
2006 was a big year for the WRX. It got its third face in five years, replacing 2004 and 2005's Blobeye design with the Tribeca-inspired Hawkeye front end, and bumped its displacement up from the 2.0-liter EJ20 to the 2.5-liter EJ25. While the new engine didn’t gain much peak power, responsiveness is said to have been massively improved in the switch.
While 2006 was a boon for the WRX, it was actually a bit of a hard year for the EJ25 as a whole. For the two years prior, it had only showed up in less-famous performance trims — the Forester, Baja, Outback, and Legacy all got it, but they didn’t have quite the same setup that the WRX did. For 2004 and 2005, the EJ255 was essentially a detuned STi EJ257 — different compression and heads, shared with Subaru’s highest performer rather than the WRX. A smaller turbocharger and different intercooler, however, prevented those cars from making STi power.
The EJ255 has some of the best aftermarket support of any tuner engine, with parts available from both Subaru and third-party suppliers. A wide array of off-the-shelf tunes from companies like Cobb make it easy to build these up to truly impressive power numbers — for a short period of time, anyway.
Beyond the common EJ issues shared with the two-liter engines, the 255 brings some new problems to the party. The plastic intercooler end tanks are known to separate and leak boost (generally above 18 psi on a factory turbo), and the connector from the intercooler to the throttle body doesn’t hold up much better. Oil filters built into the banjo bolt fitting on the turbocharger’s oil feed line are known to clog, leaving your turbo free of any lubricant. This can lead to broken impellers, metal shavings entering the oil supply, and you finding yourself trying to lift the engine just a couple inches out of your friend’s Legacy GT at midnight in December in Massachusetts to get enough clearance above the subframe to pull the oil pan. Ask me how I know.
Speaking of oil issues, watch out for cracks in the EJ255's oil pickup. Replacement units from Killer B or IAG are a common swap. Early Legacy GTs and Outback XTs had issues with fuel injectors failing, and their odd side-feed setup means they can’t easily be swapped for injectors from later models.
The most famous issue on the EJ255, however, is ringland failure. The pistons themselves crack, and can no longer hold piston rings correctly — you lose compression, oil makes its way into the combustion chambers, dogs and cats living together. This usually happens when the engine (particularly cylinder 4) is running too lean, too hot, and some have theorized that the factory exhaust manifolds that give the boxer its burble are partially to blame.
Remember at the top of the EJ section, when we talked about unequal length headers and the different distances they force exhaust gas pulses to travel before exiting the tailpipe? The theory goes that these unequal lengths mean that the exhaust pulses from cylinders 2 and 4 reach the car’s O2 sensor at vastly different temperatures than cylinders 1 and 3. The difference in temperatures and densities of exhaust pulses between the left and right cylinder banks force the car’s ECU to make air-fuel ratio adjustments based on a middle ground — meaning two cylinders run rich, and two run lean.
Has this ever been proven? Not really, though many point to Subaru’s use of equal-length headers in more recent cars as evidence of the theory’s merits. Swapping the factory manifold on the EJ255 is seen as a reliability modification for these cars, though that may simply be wishful thinking.
The USDM STi Engine: EJ257
Found in: 2004-2014 Subaru Impreza WRX STi, 2014-2021 Subaru WRX STI
The golden child of Subaru’s U.S. lineup. No engine makes more power than the venerable EJ257, and it’s found (in different versions) in everything from the earliest blobeye STi to the most powerful S209. The EJ257 gets unique heads from the later 255s, and runs at a lower compression — allowing for slightly more safe boost. In factory trim, it’s paired with a larger turbocharger than Subaru ever shipped with the EJ255.
In 2008, the engine was upgraded with newer heads, though compression didn’t change. Over the next two years, Subaru gave it a new, stronger crankshaft and upgraded connecting rods to match. Later revisions included the Type RA block, with stronger pistons and connecting rods. Starting in 2019, all WRX STIs got the upgraded Type RA variant of the EJ257 — sort of a swan song for the engine’s fifteenth birthday.
The issues with the EJ255, including those inherited from the other EJ series engines, persist here. But while spun bearings and cooked ringlands are still risks, proper tuning can help stave them off — and owners can enjoy the heightened power levels that the modern EJ257's upgraded internals can hold.
The EZ Series
Found in: Subaru Tribeca (all years), 2008-2019 Subaru Legacy 3.0R/3.6R, 2000-2019 Subaru Outback 3.0R/3.6R
Subaru may be famous primarily for its four-cylinder engines, but don’t sleep on the EZ-series six-cylinder mills. One formed the basis for the famed Mighty Car Mods Supergramps build, where it was paired with E85 and a custom turbo kit to make over 400 horsepower at the wheels.
The EZ engines, available in 3.0-liter and 3.6-liter guise, are known to be reliable if somewhat uninteresting powerplants. They forego the EJ’s problematic timing belt for a timing chain, and their natural aspiration means no issues with leaking turbos, intercoolers, or inlets. Some oil leaks are to be expected from the valve and timing chain covers, but they shouldn’t match the “valve cover gasket that drops oil directly onto the headers so your car starts smoking at red lights” leaks of the EJ255. Voice of experience on that one.
If the EZ engines have a fatal flaw, it’s the difficulty of accessing some components. The water pump is located behind the engine cover, making replacement a time-consuming (and costly, at hourly mechanic rates) endeavor. The EZs also have issues with bearings on their serpentine belt — if there’s any noise, vibration, or wobble in the pulleys, price in the cost of replacing them.
The FB Series
Found in: 2012+ Subaru Impreza, 2012+ Subaru XV/Crosstrek, 2011+ Subaru Forester, 2013+ Subaru Legacy, 2013+ Subaru Outback
The EJ and EZ engines, beloved as they are, weren’t built to last forever. Modern innovations in engine design, injection systems, and emissions equipment eventually forced them to the sidelines. Their replacements, the FA and FB series engines, are new enough that some mechanical faults may still be unknown — but many have shown reared their heads already.
We’ll tackle the FB series engines first, as they’re the more standard commuter fare. The FA engines, including the now-standard FA24F turbocharged mill that replaces the EJ255, EJ257, and the EZ engines, will come after. Save the best for last, right?
The Modern Commuter 2.0-Liter: FB20
Found in: 2012+ Subaru Impreza, 2012+ Subaru XV/Crosstrek
Subaru has made a number of slight revisions to the FB20 engine over the years, but none have been earth-shattering. These are the first Subaru commuter engines to use direct injection, where fuel is squirted directly into the cylinder rather than before the intake valves. While this has its benefits for efficiency, it can leave the backs of the valves coated with carbon that a more standard port injection system would’ve self-cleaned. This isn’t unique to Subaru, however, and poses the same risks as any other modern direct-injected engine.
Like all flat engines that aren’t built in Stuttgart, FB20 engines commonly have small oil leaks. A larger oiling issue, however, is the oil consumption TSB that Subaru put out for both FB engines. Despite resulting from a class-action lawsuit, the issue is said to affect a small percentage of cars. Still, it’s worth checking a listing’s VIN against that TSB before signing the title.
The FB series also included three hybrid variants: the FB20X, FB20V, and FB20D e-Boxer. None are a revolution when compared to their ICE counterparts, and only the FB20V remains in production. It’s limited to a single model, the Crosstrek Hybrid, and sources much of its electric parts from Toyota. It seems... fine.
While the FB engines are largely reliable, the CVT transmissions they’re bolted to are often a source of issues. Subaru has had a few CVT issues in recent memory, and has extended the warranty on some cars to account for the problems. If you’re buying a modern Subaru, consider the stick shift. If you’re interested in this engine, you probably won’t, but I can dream.
The Modern Commuter 2.5-Liter: FB25
Found in: 2011+ Subaru Forester, 2013+ Subaru Legacy, 2013+ Subaru Outback, 2021+ Subaru Crosstrek (Sport and Limited trim levels)
If you want something that feels faster than the FB20, but is overall nearly identical, the FB25 is your bet. Still no turbo, but the FB25 adds a bit of displacement — which, while replaceable, is still nice. The FB25 is primarily offered in Subaru’s heavier vehicles, so there’s no 2.5-liter Impreza on the menu.
Issues with the FB25 carry over from the FB20. Minor oil leaks, an oil consumption TSB, but most problems are related to the CVT. When it comes to modern Subaru commuter offerings, a traditional inline layout from Toyota or Honda is likely more reliable — but, with modern cars, everything is reliable. At least with the Subaru, it’s also interesting — and has all-wheel-drive standard.
The FA Series
Found in: 2012+ Subaru BRZ, 2012-2016 Scion FR-S, 2016-2020 Toyota 86, 2015-2021 Subaru WRX, 2014-2018 Forester XT, 2022+ Toyota GR86, 2018+ Subaru Ascent, 2020+ Subaru Legacy XT, 2020+ Subaru Outback XT, 2022+ Subaru WRX
Subaru’s FB engines make for nice commuter cars, but they can’t compete in the performance market. For that, the six-star badge offers a different line of powerplants: the FA series. FA engines aren’t exclusively for performance use cases, but all performance engines Subaru makes are from the FA line.
The First Toyobaru Engine: FA20D
Found in: 2012-2020 Subaru BRZ, 2012-2016 Scion FR-S, 2016-2020 Toyota 86
Remember up top, where I said that two and a couple halves automakers use boxer engines? We’ve already touched on Saab, but Scion (RIP) and Toyota count too. The FA20D, shared with the FR-S and 86, is unique among Subaru engines in that it also exists under another name: the Toyota 4U-GSE. Toyota had a hand in the FA20D’s development, lending its D-4S direct-and-port-injection system, and for that input the company earned the right to revive the U-series flat engine moniker it abandoned in the ‘70s.
The FA20D is famous for its torque dip, the total loss of any feeling of acceleration in the middle of the rev range — you know, where your engine spends much of its non-highway time. That can be solved with headers, or with the judicious application of forced induction. The latter, however, will feed one of the FA20D’s other demons.
Regardless of chassis or grille shape, the FA20D runs hot. These engines burn up coil packs and thin out oil like it’s their job. It’s gotten to the point where an oil cooler is almost seen as a mandatory track-day accessory on the forums. The loss of oil pressure that comes at high heat and high revs in these engines is known to cause on-track failures, so go up a couple oil weights before your next HPDE. Superchargers and (especially) turbochargers compound the issue, so give the next BRZ you see with a vented hood a break. It may well be functional.
2012 and 2013 FA20D engines were recalled for valvetrain issues, to replace valve springs. For many cars, however, the cure proved to be worse than the sickness. Reports flooded in of engines failing just hundreds of miles after the fix, with issues primarily facing the Scion side of things. The leading theory, backed up by a few teardowns of failed engines, is that the techs in Scion dealers simply weren’t used to applying sealant to the unique boxer layout. Too much sealant was applied when reassembling the engines, and it found its way down into the oil pan — and clogged the pickup. If you’re looking at buying one of these cars, avoid the 2012 and 2013 models if you can.
At high RPM, these engines also risk losing their rocker arms. When fully wrung out to redline, the rocker arms can come unmoored from their location in the valvetrain — and, in the worst cases, exit through the valve cover.
The Return Of The 2.0-Liter WRX Engine: FA20F
Found in: 2015-2021 Subaru WRX, 2014-2018 Forester XT
Ah, the FA20F. The engine that powered the least-loved yet best-selling generation of the WRX since the previous one — at least, until Subaru introduced an even-less-loved generation last year that will probably sell even better. The FA20F brought the WRX back to its two-liter roots, but introduced direct injection to the party.
These engines are largely reliable in stock form, but can go downhill when tuners try to add too much power. The FA20F’s weak point is its connecting rods, which can let go when drivers demand high boost at low RPM. That request can be damaging in any modern turbocharged engine, so remember to roll on the gas rather than matting the throttle from a standstill. Your connecting rods will thank you.
Like other direct injected turbo engines, the FA20F can fall victim to low-speed pre-ignition. If you’ve ever wondered why so many cars require 91 octane now, heightened octane is a preventative measure against LSPI. Engine oil formulas are also said to have an effect, so don’t give your WRX the cheap stuff.
Aftermarket exhausts, oddly enough, are known to make this generation of WRX spit smoke. The issue comes from the turbocharger itself: Decreased exhaust backpressure means there’s less force pushing on the turbo’s oil seals, allowing some amount to leak out into the exhaust. The solution is a turbo sump restrictor, which aids in evacuating oil from the turbo before pressure can build up.
The Second Toyobaru Engine: FA24D
Found in: 2022+ Subaru BRZ, 2022+ Toyota GR86
The FA24D made its debut appearance in the updated 2022 BRZ and GR86. It retains the Toyota-sourced D-4S injection system from the FA20D, but widened the smaller engine’s famous 86mm bore out to 94mm. It’s said to eliminate the old engine’s torque dip, or at least mitigate the worst of its effects.
The FA24D also addressed another of the FA20D’s biggest shortcomings by adding a factory oil cooler. While it’s not a true liquid-to-air cooler, instead cooling the oil with coolant from the engine block, it should help bring oil temperatures back down from their peaks more quickly — even if it won’t do much to keep them down under load.
Since the FA24D is just barely starting to make its way into the hands of owners, not much is known about its reliability yet. However, given the amount of engineering shared with the FA20, expect many of the same warnings to apply.
The Modern Turbo Mill: FA24F
Found in: 2018+ Subaru Ascent, 2020+ Subaru Legacy XT, 2020+ Subaru Outback XT, 2022+ Subaru WRX
Here it is, Subaru’s modern golden child. Gone are the EJ207 and 257, the FA20F and the EJ255. This is Subaru’s new turbo engine, singular. While the company hasn’t yet confirmed the engine’s use in an updated STI, it’s implied that this is simply The Turbo Subaru Engine now. Expect a dynamic more akin to the EJ255/EJ257 divide than anything too dramatic.
The FA24F made its first appearance in the Ascent, leading many to deride it as “just a crossover engine” when it was announced for the WRX. The counterpoint, however, is that those years in the Ascent served as a test bed — now, it’s ready for performance applications.
Much like the FA24D, the FA24F is too new to have a definitive list of common problems and their solutions. As the next few years wear on, however, expect these to show up in the hands of thousands of tuners with more money than sense. That, it seems, is the true test of an engine’s reliability: How well it can resist the whims of an uncaring owner.
Should You Buy A Boxer?
At the end of the day, it’s up to you. Subaru’s flat-four and flat-six engines are known for their low centers of gravity, expansive aftermarket support, and fantastic sound. The turbocharged four-cylinders, with their relatively high displacement (save for the FA20F), have genuinely exciting powerbands that can make you feel like Colin McRae in any snowy parking lot. Trust me, I’ve owned two, I get the appeal.
But I also get the folders full of maintenance receipts, the trial-and-error of finding a shop that really understands the unique layout, and the emails from my credit card company saying “Hey, did you mean to spend this much on parts and labor?” The benefits of a boxer engine don’t come for free, and there are reasons Subaru is the only manufacturer to exclusively use the design. Boxers are heavier, more mechanically complex, and harder to work on than a traditional inline or V engine layout. Working on them yourself requires a lot of unique knowledge, and taking one to a shop means doing the research to find a mechanic who won’t fill your oil passages with sealant.
Like all engine layouts, Subaru’s boxers have pros and cons. With any luck, after reading the past 4,500+ words, you’ve gotten a taste of what those are — and whether your own yellow legal pad of factors stacks more towards the positives or the negatives.