Subaru EJ257 Engine Problems, Reliability, Specs, Tuning

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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. These engines produce a lot of power for just a small 2.5L engine and they are popular to modify. However, the big downside is that they just aren’t that reliable, especially when you start tuning them.

Once you add tuning and some bolt-on modifications, the EJ257 becomes prone to turbo failure, oil leaks, and engine failure caused by issues with the rods, pistons, bearings, and ringlands.

In this guide we’re going to cover everything about the reliability and problems of the EJ257 both stock and when combined with performance upgrades. We’ll also briefly discuss the most common mods and the factory performance specs.

Engine Specs

LayoutFlat-four (4 cylinder)
Displacement2,457 cc (2.5L)
Head/Block MaterialAluminum
ValvetrainDOHC, 16 valve
Bore x Stroke99.5mm x 79mm
Compression Ratio8.2 : 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 engine to deliver great performance for its size. Aluminum heads and block help keep weight down.

These engines are very similar to their EJ255 brothers, both in reliability and common problems.

Vehicle Applications

  • 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 WRX STI EJ257 Problems, Specs, Reliability

Subaru EJ257 Tuning & Mods

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 to the next level. Some of those mods include:

  1. Tune
  2. Intake
  3. Downpipe / Exhaust
  4. Intercooler
  5. Fueling / Methanol Injection (WMI)

What’s most important is how these performance upgrades play into reliability, considering the EJ257 isn’t the strongest engine around and is known to fail pretty easily with upgrades.

Tuning & It’s Impact on Reliability

All else equal, adding more boost and power is going to put more stress on the 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.

These engines can suffer from a number of issues with the internals. From the rods, to bearings, pistons, and ringlands, the internals are problematic. While they do sometimes cause problems on stock STi’s, they become way more 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 STi, though. Therefore, it can be a bit of a concern when going that route.

Subaru EJ257 Engine Problems

  • Turbo Failure
  • Internal Problems
  • Oil Leaks

1) Turbo Failures

First up is an issue that’s typically due to tuning and upgrading the EJ257 engine. Turbo failures can and do occur on stock engines. This is especially true on some older 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. 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.

2) 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).

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 tend to happen. 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 likelihood of failure a bit more than the older versions.

3) 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 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.

Overall 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 engine is plagued by endless problems. But more-so that there are a few pretty severe and costly issues that occur 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 these engines 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 them 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.

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