The 2004 Impreza WRX STi was the first vehicle to use Subaru’s EJ257 2.5L turbo engine. The WRX STI models continue to use it today. The popularity of flat-four engines is well-founded. Other than the EJ257 engine, the STI models have a lot to offer, but that isn’t the point. EJ257 engines have a power range of 300-341 hp and 290-330 lb-ft of torque.
Excellent performance for a 2.5-liter flat-four engine of this size. The Subaru EJ257 engine is examined in depth in this guide, which covers a wide range of topics such as problems, reliability, specifications, and aftermarket modifications.
What Cars Use the EJ257?
It’s a short list because the 2.5 EJ257 engine primarily powers the Impreza WRX STi and WRX STI. There are a few exceptions to this rule, however. The following automobiles use EJ257 engines:
- 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)
Subaru’s EJ257 engine designation is reserved exclusively for the STI. However, the 2.5L STI engine was used in the Forester XT, Outback XT, and Legacy GT models. The turbo, intercooler, and factory tune were all gone from the EJ257 engine.
Subaru EJ257 Engine Specs
The following are the technical specifications for the EJ257 flat-four boxer engine:
|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 flat-four cylinder design of the EJ257 makes it unique. Only a few other companies make engines with this layout. It contributes to the distinctive sound of many Subarus. Regardless, a 2,457 cc engine has a displacement of 2.5 liters.
The EJ257 STi engines’ performance is enhanced by the addition of a turbocharger. By using aluminum for the heads and block, you’re able to reduce the overall weight.
It has a low compression ratio and a 16-valve DOHC over-square design. Subaru EJ257 engines are capable of 300-341 hp and 290-330 lb-ft of torque with all of these specs.
EJ257 2.5 Turbo Tuning & Mods
An article on tuning and mods for the EJ257 will be forthcoming. However, in this article, we’ll go over the fundamentals. The EJ257 WRX engine’s reliability and problems are very similar to those of the EJ257. This article will cover EJ257 issues, but in a more condensed manner than usual. As a result, we’ll spend a few minutes talking about tuning and mods. Let’s get started right away.
In the rally car world, Subaru models like the WRX STI are well-known for their racing heritage. The 2.5L flat-four turbo engine powers these fun machines all around. The factory-installed power is already impressive at 300+ hp.
However, with a tune and a few simple modifications/upgrades, the STi EJ257 engine can really be taken to the next level. Here are a few examples of customizations:
- Downpipe / Exhaust
- Fueling / Methanol Injection (WMI)
In the near future, we’ll go into greater detail about these modifications. In spite of this, the aforementioned modifications will significantly improve the performance of the EJ257 2.5 turbo engine. For those who want to push things even further, turbo upgrades are an option. When you have a lot of money, the sky is the limit. But how does all of this relate to the issues with the EJ257 engine’s reliability?
WRX STI Tuning & Reliability
Adding more boost and power will, on balance, tax the 2.5-liter flat-capacity. four’s The internal strength of the EJ257 engine isn’t well-known. With a good setup, they can run on a stock engine and be dependable.
Nevertheless, tuning and modifications to Subaru WRX STI models are quite common. When purchasing a pre-owned vehicle, you have no idea how the previous owner treated it.
We’ll go over a few of these internal problems in more detail under the “engine problems” heading. They can occur in cars that are completely stock. Nevertheless, the majority of these problems can only be found in EJ257 engines that have been modified.
The point is that tuning, modding, and upgrading these engines is fairly common. When done correctly, an EJ257 can last for many years. Used WRX STIs, on the other hand, aren’t always transparent about what you’re getting. As a result, if you choose to go that route, you may have some reservations.
Subaru EJ257 Engine Problems
The following are some of the most frequently encountered Subaru EJ257 engine issues:
- Turbo Failure
- Internal Problems
- Oil Leaks
Many of these issues were also discussed in our article on the WRX EJ255 engine. However, there are a few minor differences between the EJ257 engine’s issues and those with the EJ254. In any case, these are some of the more common problems.
This does not imply, however, that they are widespread in the real sense of the word. Instead, these are some of the most common locations where Subaru EJ257 engine issues occur.
As a result of this, the 2.5-liter STI flat-four engine has proven to be dependable and long lasting. Even though the engine isn’t unreliable, there are a few issues that can be costly to fix. At the conclusion of this article, we’ll return to the subject of EJ257 reliability. While we wait for that to happen, let’s take a look at the previous failures.
1) Subaru WRX STi Turbo Failures
We’ll start with something that happens when you tune or upgrade your EJ257 flat four engine. On stock engines, turbo failures are possible and have occurred. On some older EJ257 turbo engines, this is especially true.
The WRX STI’s turbocharged engine has been around since 2004 and has seen better days. As a result, natural failures can occur simply as a result of advancing age.
On the other hand, the Subaru EJ257 engine can be tuned or modified. As a result, the turbo’s boost pressure must be increased, further taxing it. If you don’t overdo it, the turbo will last a while longer. The STI’s turbocharger will have a shorter lifespan if you increase the boost, so be careful when doing so.
With stock boost, the turbo is unlikely to fail before 125,000 miles or more. As you increase the boost, the turbo’s lifespan will deteriorate. Some of them could last up to a million miles. Other EJ257 turbos may fail before the 50,000-mile mark, depending on driving conditions. Although it’s not a perfect science, the general gist of it holds true.
EJ257 Flat-Four Turbo Failure Symptoms
The following symptoms may indicate that the EJ257 2.5 turbo is malfunctioning or failing:
- Smoke from exhaust
- Whining turbo
- Power loss
If your turbos start to fail, you’ll notice that the engine starts to smoke and burn oil. When one of our BMWs had a turbo failure, over 5 liters of oil were spewed out the exhaust. This was a one-off failure, not indicative of a trend in turbo failures over time. Even so, a malfunctioning turbo can waste a significant amount of oil.
The EJ257 turbocharger’s louder whining sounds may also be an indication of a problem. It’s understandable that a damaged turbo won’t be able to produce as much boost as desired. As a result, there will be a noticeable drop in power.
WRX STI Turbo Replacement
The cost of replacing a turbo is high due to the high cost of the parts and the time it takes to complete the job. It is possible to find used turbos for less than $500, but doing so is fraught with danger. Otherwise, a brand-new OEM EJ257 turbocharger will set you back more than $a thousand dollars. That’s also the cost of most direct bolt-on turbo upgrades.
The time it takes to replace the turbo on a WRX STI is typically between $400 and $600. DIY’ers can save a lot of money by doing it themselves, but it requires a moderate level of mechanical ability. If you’re familiar with the EJ257 engine, this job should be a cinch.
2) Subaru EJ257 Internal Engine Problems
EJ257 problems are all too common on modified engines, and this one is no exception. Some lawsuits have been filed in relation to Ringland issues, which are a hot topic (along with other internal failures). While thinking about WRX STi engine failures is never pleasant, we believe the incidents are exaggerated. However, the failures of the EJ257 internal engine remain a significant issue.
With a tune and bolt-on modifications, a good friend of ours blew up an EJ255 WRX and an EJ257 STI. If we are to believe his failures, we must remember he was far from an expert and made a number of mistakes.
On the other hand, it serves as a timely reminder about how forgiving the EJ engines can be. Mistakes in tuning, pushing things too far, and so on can have expensive repercussions.
Anyway, the 2.5L flat-four engines have a history of failures. Many different types of parts are used in engines. The piston design on the 2019 and later WRX STI models has been updated, as have some other valvetrain improvements. Time will tell if this reduces the frequency of internal engine issues.
EJ257 2.5L Internal Issue Symptoms
When the Subaru EJ257 2.5 boxer engine’s internal components fail, the following symptoms may occur:
- Smoke from exhaust
- Compression loss
- Knocking / ticking
- Loss of oil pressure
- Excess oil consumption
This is a short list of notable figures. When an engine fails or starts to fail, there are numerous symptoms that could occur. Excessive oil pressure and smoke are caused by the piston rings and ringlands being able to pass more oil through them.
Excessive oil consumption and other symptoms are frequently associated with rod bearings. Sounds like knocking, pinging, or ticking could indicate a problem with the EJ257 engine’s internals.
Subaru EJ257 Internals/Engine Replacement
Failures can occur at any time, but sometimes you’ll be able to detect them in time. Even if you fail to detect an EJ257 rod bearing failure in time, it may not cause too much damage. You’ll still have to spend money on new bearings. A failed rod bearing can damage the crank, causing rods to knock and pistons to bang against the cylinder wall.
Internal problems may, in the end, lead to engine failure. Engine rebuilding is almost always more expensive than simply installing a new, used one. The bottom line is that EJ257 engine failures are extremely expensive to repair.
3) EJ257 STI Oil Leak Issues
Fortunately, the Subaru EJ257 doesn’t have any major flaws that could lead to oil leaks. On many cars and engines however, this is a common problem. This is primarily because many WRX STI engines are over eight years old.
Rubber or rubber-like materials are frequently used in the manufacture of gaskets, seals, rings, and other mechanical seals. Over time, they harden, crack, and let small amounts of oil seep through. Those oil leaks can get worse over time. EJ257 STI oil leaks are frequently caused by blown valve cover gaskets (BVG).
Valve cover gaskets are far more common than oil pan and main seal leaks. As a general rule, expect leaks to appear after 8 years or 100,000 miles of driving. When a gasket fails, it’s usually due to wear and tear or mileage, not a design flaw.
Subaru EJ257 Oil Leak Symptoms
The following are some signs of an oil leak on a Subaru WRX STI:
- Visible oil leak
- Engine bay smoking
- Burning oil smell
- Oil in spark plug holes
- Low oil
A common and obvious symptom is an oil leak that can be seen in the engine’s coolant. Some oil leaks, however, do not result in spills. If the EJ257 oil leak is only a small amount, oil may become trapped on the block and other components.
Additionally, it has the potential to drip onto hot components and burn off, resulting in smoke and the smell of burning oil. VCG leaks frequently occur in this manner.
While changing spark plugs, keep an eye out for any signs of valve cover gasket leakage, which can lead to oil getting into the spark plug chamber. Low oil levels, on the other hand, may indicate an oil leak. Since an oil leak would have to be extremely severe, that is unlikely to be the first symptom you encounter.
2.5 Flat-Four VCG Oil Leak Fix
For a total of less than $50, you should be able to purchase both of your valve cover gaskets from the same source. The Subaru EJ257 2.5L engine’s valve cover gasket replacement requires several hours of work. As a result, expect to pay in the range of $200-400 for repairs.
It’s not a difficult DIY project, but it’s critical to make sure the gaskets are properly sealed before moving on. If you don’t, you’ll probably be back on the job in a few weeks.
Subaru EJ257 Reliability
Is the EJ257 engine in the Subaru WRX STI dependable? The EJ257 has a reputation for being unreliable. The 2.5L Subaru boxer engine doesn’t have a lot of issues. However, the EJ257 is more prone than the average engine to a few serious and expensive problems.
The driving style, modifications, and tuning of the average WRX STi all play a role. These automobiles are popular among buyers who plan to customize them. The EJ257 can be finicky if you don’t know what you’re doing. In terms of abuse, errors, and poor tuning, some engines can take it. We don’t think the Subaru EJ257 falls into this category.
All things considered, the EJ257 is a dependable engine with a respectable lifespan. As with any engine, routine maintenance is critical. Make sure to use high-quality oils, keep an eye on the oil level, and so on.
If you’re going to tune the WRX STI EJ257 engine, make sure it’s dialed in first. The Subaru EJ257 engine, when configured correctly, can be a dependable and a lot of fun to drive.
Which WRX STi engine do you have experience with? Is one something you’re thinking about doing?
Let us know what you think by leaving a comment below!
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