The Subaru EJ257 2.5L turbo engine made its debut in the 2004 Impreza WRX STi. It’s still in use in the WRX STI models to this day. Many love these flat-four boxes engines for good reason. The STI models also have plenty to offer outside of just the engine, but that’s beside the point. EJ257 engines deliver 300 to 341 horsepower and 290-330 lb-ft. Excellent numbers for a relatively small 2.5L flat four boxer engine. In this guide, we explore the Subaru EJ257 engine and cover problems, reliability, specs, mods, and more.
Subaru EJ257 Engine Specs
Specs for the EJ257 flat-four boxer engine are as follows:
|Layout||Flat-four (4 cylinder)|
|Displacement||2,457 cc (2.5L)|
|Valvetrain||DOHC, 16 valve|
|Bore x Stroke||99.5mm x 79mm|
|Compression Ratio||8.2 : 1|
|Torque (lb-ft)||290-330 lb-ft|
The EJ257 is unique in its flat four cylinder design. Few other manufacturers use this engine layout. It’s part of what gives many Subaru’s a unique sound. Anyways, the 2,457 cc displacement rounds up to 2.5 liters. A turbo delivers boost to allow the EJ257 STi engines to deliver great performance for their size. Aluminum heads and block help keep weight down.
Add in it’s 16 valve DOHC, over-square design with a low compression ratio. All of these specs make the Subaru EJ257 engines good for 300-341 horsepower and 290-330 lb-ft of torque.
What Cars Use the EJ257?
It’s a pretty short list as the 2.5 EJ257 engine is primarily in the Impreza WRX STi and WRX STI models. However, there are a few exceptions. EJ257 engines are in the following models:
- 2004-2007 Impreza WRX STi (300hp)
- 2008-2018 Impreza WRX STI (305hp)
- 2019-current WRX STI (310hp)
- 2019 STI S209 (341hp)
- 2005-current Impreza WRX STi (276hp, non-US models)
- 2004-2005 Forester XT (210hp)
- 2005-2006 Legacy GT / Outback XT (250hp)
From Subaru the STI is the only model to receive the EJ257 engine designation. Forester XT, Outback XT, and Legacy GT models actually did use the 2.5L STI engine, though. They were the same as the EJ257 engine less the turbo, intercooler, and factory tune.
EJ257 2.5 Turbo Tuning & Mods
Tuning and mods for the EJ257 is a topic we’ll tackle in greater depth in a future article. However, we decided to cover some of the basics in this article. EJ257 engine problems and reliability are actually similar to the EJ255 WRX engine. We’ll cover EJ257 problems in this article, but in a shorter hand format that usual. As such, we have a little time to cover some tuning & mod info. Let’s jump right in.
Subaru WRX STI models are well known for their rally car heritage. They’re fun cars all around, but the 2.5L flat-four turbo engine is the heart. 300+ horsepower from the factory is already pretty stout. However, a tune and a few basic mods/upgrades can really take the STi EJ257 engine to the next level. Some of those mods include:
- Downpipe / Exhaust
- Fueling / Methanol Injection (WMI)
Again, we’ll cover these mods in-depth in the near future. Nonetheless, the above mods can easily boost the EJ257 2.5 turbo engine to a whole new level. Turbo upgrades are also a common choice to take things even further. The sky is the limit with deep pockets. How does all of this tie into EJ257 engine problems & reliability, though?
WRX STI Tuning & Reliability
All else equal, adding more boost and power is going to put more stress on the 2.5 flat-four engine. The EJ257 isn’t known to be the strongest engine internally. They can be reliable on the stock engine with a good setup. However, tuning and mods are so common on Subaru WRX STI models. If you’re buying used it’s hard to know how the previous owner took care of the car.
In the engine problems section we’ll be discussing a few of these internal issues. They can happen on totally stock cars. However, many of these issues are most common on modded EJ257 engines.
Point is – these engines are common to tune, mod, and upgrade. When done right you can have an EJ257 that’s reliable for the long-term. It’s not always clear what you’re getting if you buy a used WRX STI, though. Therefore, it can be a bit of a concern when going that route.
Subaru EJ257 Engine Problems
A few of the most common problems with the Subaru EJ257 engine include:
- Turbo Failure
- Internal Problems
- Oil Leaks
Again, we went over a lot of these issues in an article about the WRX EJ255 engine. Problems on the EJ257 engine are similar, but there are some minor differences. Anyways, we’re considering these among the most common issues. That doesn’t necessarily mean they’re common in the true sense of the word. Rather, when Subaru EJ257 engine problems occur these are a few of the most frequent areas.
That said, the 2.5L STI flat four engine can provide solid reliability and longevity. It’s not an unreliable engine, but a few of the issues can be pretty serious and costly. We’ll circle back to the EJ257 reliability topic at the end of the article. Until then, let’s move on and examine the above failures.
1) Subaru WRX STi Turbo Failures
First up is an issue that’s typically due to tuning and upgrading the EJ257 flat four engine. Turbo failures can and do occur on stock engines. This is especially true on some older EJ257 turbo engines. The engine has been around since 2004 in the WRX STI; high age and mileage can take a toll on a turbo. As such, some natural failures simply occur because of age.
On the other hand there’s tuning and modding the Subaru EJ257 engine. This usually calls for increasing turbo boost pressure, which puts more stress on the turbo. Unless you’re pushing things too far it’s not going to kill the turbo immediately. However, increasing boost can shorten the lifespan on the STI’s turbocharger.
With stock boost it’s pretty uncommon for the turbo to give out before 125,000+ miles. Add in more and more boost and the turbo likely won’t last as long. Some may hold up for 100,000+ miles. Other EJ257 turbos may let go earlier than 50,000 miles. It’s not a perfect science, but the general point remains.
EJ257 Flat-Four Turbo Failure Symptoms
The following symptoms may point to a problems or failure of the 2.5L turbo:
- Smoke from exhaust
- Whining turbo
- Power loss
As turbos fail they may begin burning oil and you’ll notice smoke from the exhaust. Heck, when one of our BMW’s blew its turbo the engine dumped over 5L of oil into the exhaust. That was a drastic, sudden failure and isn’t relative to longer-term turbo failures. Nonetheless, a turbo can burn/dump a lot of oil if it’s not functioning properly.
Louder whining turbo sounds can also indicate a problem with the EJ257 turbocharger. Of course, a turbo in poor shape might not reach the target boost levels. This will lead to noticeable power loss.
WRX STI Turbo Replacement
Replacing a turbo isn’t a cheap job since they’re expensive parts and can take a bit of labor. Used turbos can be found for less than $500 sometimes, but that can be a bit risky. Otherwise, a new OEM EJ257 turbo is going to run $1,000+. That’s also the price point for most turbo upgrades that are a direct bolt-on fit.
Labor to replace the WRX STI turbo is usually in the 3-6 hour ballpark, so add in another $400-600+ in labor. DIY’ers can save some good money there, but it’s a job for moderate or better mechanics. If you know you’re way around the EJ257 engine it’s a pretty simple job.
2) Subaru EJ257 Internal Engine Problems
Yet again, this is another one of the EJ257 problems that’s most common on modded engines. Ringland issues are a hot topic and there have been some lawsuits regarding that (along with other internal failures). It’s never fun to think about WRX STi engine failures, and we believe they are slightly blown out of proportion. EJ257 internal engine failures are still an important topic, though.
A good friend of our blew up an EJ255 WRX and EJ257 STI with a tune and bolt-on mods. It’s safe to say he wasn’t an expert and made some errors, so we take those failures with a grain of salt. However, it is a reminder that the EJ engines aren’t the most forgiving around. Small tuning mistakes, pushing things too far, etc. can lead to costly consequences.
Anyways, there are a number of failures that occur on the 2.5L flat-four engines. Rods, rod bearings, pistons, and ringlands are among the most common. 2019+ WRX STI models do have an updated piston design and some other valvetrain upgrades. Time will tell if this helps make these internal engine problems occur less often.
EJ257 2.5L Internal Issue Symptoms
Symptoms of internal engine failures on the Subaru EJ257 2.5 boxer engine include:
- Smoke from exhaust
- Compression loss
- Knocking / ticking
- Loss of oil pressure
- Excess oil consumption
This is a relatively short list. There are lots of potential symptoms when an engine fails or begins to fail. More oil can pass the piston rings and ringlands causing smoke and excess oil pressure. Rod bearings often result in excess oil consumption among other symptoms. Knocking, pinging, or ticking sounds can all point to EJ257 internal engine problems.
Subaru EJ257 Internals/Engine Replacement
Depending on the failure in question you may be able to catch it in time. For example, EJ257 rod bearing failures may not cause too much damage if you catch the problem before it comes severe. You’ll still need to replace the bearings which can be expensive. However, if a rod bearing completely fails it can dig into the crank, cause rods to knock, pistons to slap on cylinder walls, etc.
Ultimately, internal issues can result in complete engine failure. Even if the engine can be re-built it’s likely to be as much or more expensive than dropping in a new, used engine. Point is – EJ257 engine failures are costly.
3) EJ257 STI Oil Leak Issues
Fortunately, there aren’t any major design flaws with the Subaru EJ257 that cause oil leak problems. It is, however, a common issue on many cars and engines in general. We’re mostly including this topic since many WRX STI engines are 8+ years old.
Gaskets, seals, rings etc are often made from rubber or rubber-like materials. Over time, they harden, begin cracking, and develop small oil leaks. As time passes those oil leaks can become much worse. Valve cover gaskets (VCG) are among the most common EJ257 STI oil leaks.
Oil pans and main seals are a few other areas, but valve cover gaskets appear much more common. Anyways, look for these leaks to primarily develop after 8+ years and 100,000+ miles. Gasket failures can occur sooner, but it’s usually an age/mileage issue rather than a flaw.
Subaru EJ257 Oil Leak Symptoms
A few symptoms of oil leaks on the WRX STI are as follows:
- Visible oil leak
- Engine bay smoking
- Burning oil smell
- Oil in spark plug holes
- Low oil
Visible oil leaks are one of the most common and obvious symptoms. However, not all oil leaks result in oil dripping to the ground. Sometimes the EJ257 oil leak may be minor enough that oil sticks to the block and other parts. It may also drip onto hot parts and burn off, which leads to smoke and burning oil smells. This is common for VCG leaks.
Valve cover gasket leaks often result in oil getting into the spark plug chambers, so look out for that when changing spark plugs. Otherwise, low oil can point to an oil leak. It’s unlikely that will be the first symptom you’ll notice since an oil leak would need to be pretty drastic.
2.5 Flat-Four VCG Oil Leak Fix
Valve cover gaskets are dirt cheap and you should be able to source both for less than $50 total. Replacing valve cover gaskets on the Subaru 2.5L engine is a couple hours or more labor. As such, a repair shop will likely charge somewhere in the $200-400 ballpark.
It’s not a super challenging DIY but it’s important to ensure the gaskets seal properly. If not, you might find yourself doing the job again within a few weeks.
Subaru EJ257 Reliability
Is the Subaru WRX STI EJ257 engine reliable? We’re inclined to say the engine offers below average reliability. It’s not so much that the 2.5L Subaru boxer engine is plagued by endless problems. However, there are a few pretty severe and costly issues that occur on the EJ257 more frequently than the average engine.
A big part of this is likely the driving style, mods, and tuning on the average WRX STi. Many people buy these cars and mod them. Not everyone knows what they’re doing, and the EJ257 can be a bit sensitive. There are engines that can tolerate a lot of abuse, errors, poor tuning, etc. The Subaru EJ257 is not one of those, in our opinion.
All that said, the EJ257 can be a reliable engine that provides average longevity. Maintenance is one of the big keys as with any engine. Use high quality oils, check oil levels, change fluids on time, so on so forth. If you plan to tune the WRX STI EJ257 engine then ensure you have a well setup and dialed in tune. When things are done right the Subaru EJ257 can be a reliable and extremely fun engine.
What’s your experience with the WRX STi engine? Are you considering one?
Leave a comment and let us know!