4 Most Common Subaru EJ255 Engine Problems

EJ255 Subaru engines are 2.5L turbo flat four engines found in several 2004-2014 US models. The engine is still in use in other parts of the world, as of 2020. It’s a strong engine from the factory producing 210-265 horsepower. These engines are also well known for responding well to tuning and mods. The EJ255 really is a solid overall engine. However, no engine is perfect and there aren’t any exceptions here. In this guide, we discuss a few common Subaru EJ255 problems and reliability.

Subaru EJ255 Engine Problems

A few of the common EJ255 issues include:

• Turbo failure
• Valve cover gasket oil leaks
• Ringland problems
• Rod bearing failure

A few quick notes that we’ll expand on later in this article. Simply because we’re calling these common problems does not mean a majority of cars will have the issue in question. Additionally, these engines are aging so many problems are fair game. The occasional oil leaks, cooling system problems, etc. can and do occur on Subaru EJ255 engines.

We’ll expand on the above problems throughout the rest of this post. It’s important to note – some of these problems become more common as you tune and modify the EJ255. Keep that in the back of your mind if you intend to add some bolt-on mods to your Subaru. That said, some problems may appear more common on models like the Impreza WRX. A lot of that can likely be chalked up to more Subaru WRX’s being modded compared to Forester’s, for example.

1) Turbo Problems

There are a few causes of turbo problems and failure on the EJ255 engine. Before we dive into the actual failures that have an underlying reason let’s discuss age. Most Subaru EJ255 engines on the road are 10-15 years old. Turbos can last the life of a vehicle, but they are a wear and tear part. It’s not uncommon to see random turbo failures, especially at 150,000+ miles. The same could be said for any turbo engines, not just these Subaru’s. Moving onto the actual problems that may cause turbo failure.

EJ255 engines use very small oil filters. Over time, the tiny filters become clogged and the engine oil begins bypassing the filter. Subaru EJ255 turbos receive oil through a banjo bolt with a mesh screen in it. The unfiltered oil can then deposit small debris in the banjo bolt, which reduces oil flow to the turbo. A turbo with minimal or no oil flow isn’t going to fare so well. It’s a good idea to upgrade to a larger oil filter like the OEM Mazda filter that’s a direct fit for the EJ255 engine. You may also consider replacing or cleaning the banjo bolt.

In rare cases, a turbo failure may cause internal engine damage. This occurs if the turbo sheds some metal into the oil which can be picked up and pulled through the engine. Not to scare anyone, but it’s another reason keeping up on maintenance with the banjo bolt, oil filter, and oil are very important.

EJ255 Turbocharger Failure Symptoms

Look out for the following symptoms that may indicate turbo problems on the Subaru EJ255:

• Smoke from exhaust
• Louder turbo whine
• Loss of power
• Boost not reaching target

Smoke from the exhaust may point to a turbo issue. However, that may also be a symptom of other problems too. Turbo whine that’s suddenly louder than normal is usually a dead give-away that your 2.5L EJ255 turbo is having some problems. You’ll also likely notice power loss due to the turbo failing to provide enough boost.

Turbo Replacement

Turbo replacement on the Subaru EJ255 can be fairly expensive. Used turbos can be found under $1,000, but new OE turbos come in around $1,500. Labor costs can also add quite a bit extra if you’re not DIY’ing. Replacing the EJ255 turbo isn’t too complex, but it takes some time and patience. We recommend leaving turbo repairs to experienced DIY’ers or those willing to spend a weekend in the garage.

2) Valve Cover Gasket Oil Leaks

We won’t spend much time on this one. This issue is not due to any design flaws. Rather, it’s a good example of gaskets that are subject to wear and tear. The valve cover gaskets (VCG) are known to degrade and begin leaking oil with age and mileage. Since the Subaru EJ255 is a flat four engine there are two valve covers and gaskets.

Look for VCG oil leaks to typically pop up north of 100,000 miles and 10 years old. They can begin leaking sooner, though. It’s not usually an urgent repair that needs to be fixed immediately. However, oil leaks should always be addressed in a timely manner.

VCG Symptoms & Replacement

Symptoms of the 2.5L Subaru engine leaking oil include:

• Smoke from engine bay
• Visible leak
• Burning oil smells

If you’re seeing smoke from the engine bay check your EJ255 valve cover areas. A visible leak from the VCG will be a dead give-away. Otherwise, you may notice burning oil smells if the oil is dripping onto hot parts.

Replacement of the Subaru WRX EJ255 valve cover gaskets is pretty straight-forward. You’ll need to remove the coil packs, breather hoses, and the bolts holding the valve cover on. It might take a little time and patience for less skilled DIY’ers. The EJ255 gaskets are pretty cheap so it’s not a huge replacement. Although, going to a repair shop could add a few hundred in labor.

A Quick Note Before The Next Topics

Problems with EJ255 ringlands, pistons, and rod bearings are usually more common on engines with mods. These failures do occasionally occur on stock engines, especially with age and mileage. However, it’s important to understand modding your WRX EJ255 may increase the risk of these issues popping up. You can try to limit the chances with a quality, conservative tune and proper supporting mods. Maintenance and oil changes also go a long way in minimizing risk of these failures.

A proper, conservative tune may even help prevent these issues. Subaru tuned the EJ255 and EJ257 engines to run a little bit lean. That can cause issues with detonation and subsequent engine damage. However, if you’re tuning for 350+whp the risk likely balances out or becomes even higher.

3) Ringland & Piston Problems

That said, the Subaru EJ255 has 3 piston rings. There are the upper and lower compression rings along with an oil ring. The ringlands are the areas between the three piston rings on the EJ255. Piston problems usually begin with cracks on the ringlands. A minor crack isn’t a huge deal on the ringland as long as it stays that way. It’s probably not even noticeable – unless the engine is torn down.

However, over time those cracks may expand and then you end up losing a chunk off the piston, ring, or ringlands. When this happens the consequences are pretty severe. You’ll lose some, or all, compression on the cylinder in question. It may also damage cylinder walls. Point is, this is a pretty serious issue that often results in needing a new EJ255 engine. It may, however, be rebuildable depending on the extent of the damage.

EJ255 Ringland Failure Symptoms

A few potential symptoms of EJ255 ringland or piston failure include:

• Engine knocking / ticking
• Compression loss
• Power loss
• Smoke from exhaust

If you lose a chunk of the piston(s) then you might notice a ticking/knocking sound from the engine. This isn’t always the case, but can happen especially if anything is contacting the cylinder wall. The piston will no longer properly “seal” the combustion chamber so you’ll lose compression in that cylinder. That will result in power loss. Additionally, oil may blow-by the rings, enter the combustion chambers, and cause the engine to smoke.

Ringland/Piston Replacement

Best case the motor will need to be opened up to get an idea of the extent of the damage. It may be rebuildable which would require a new piston and the walls may need to be machined. If it’s not rebuildable then you’re looking at needing a new EJ255 engine. Either way, the repair bills are going to add up and this work should be left to the professionals and highly experienced.

4) Rod Bearing Failure

Another internal engine issue for the EJ255 that’s not too fun to discuss or think about. Rod bearings essentially connect the connecting rods to the crankshaft. EJ255 rod bearings take quite a bit of abuse, and they’re typically the first to give if you run into oil flow issues. Poor maintenance history and oil change intervals also increase the risk of bearing failure. The same can be said about throwing more boost and power at the Subaru EJ255 engine.

When these bearings give out they will typically cause the rods to actually knock against the cylinder walls. You could potentially blow a hole through the engine block or seize the motor. Rod bearing issues and rod knock are very serious problems no matter how you look at it. Chances are, the EJ255 engine will not be rebuildable. Even if it is, the rebuild costs will likely exceed that of finding a replacement motor.

WRX Rod Bearing Failure Symptoms

Look out for the following symptoms of rod bearing problems:

• Rod knock
• Metal shavings in oil
• Loss of oil pressure

Rod knock is a pretty disturbing sound that generally increases with RPM’s. The EJ255 likely isn’t going to sound very healthy. Bearing wear can be caught prior to catastrophic failure. Check for metal shavings in the oil or send your oil in for the occasional analysis. You may also notice a loss of oil pressure, especially on cold starts. If caught soon enough you may save your engine from become a complete loss.

Rod Bearing Replacement

If caught soon enough you might get away with simply replacing the bearings. The crankshaft should be checked for damage to ensure the rod bearings didn’t do too much damage to the crank surface. Otherwise, it may need to be machined or it may make sense to replace the entire motor. Again, this work should be left to knowledgeable mechanics and DIY’ers that know what to look for.

Subaru EJ255 Reliability

So, how reliable is the Subaru EJ255 engine? We’re hesitant to say it’s a very reliable engine since a few of the EJ255 common problems are pretty serious and expensive repairs. However, it’s important to keep in mind the internets tendency to blow some things out of proportion. These issues and failures can and do occur. Then again, proper maintenance and oil changes go a long way to preventing any internal engine damage.

Treat your Subaru EJ255 well and chances are it will reward you. If you’re in the market – look for a well maintained example. Sometimes it comes down to the luck of the draw, but that applies to any model or car brand. We don’t believe the engine is nearly as bad as some may lead you to believe. However, calling the EJ255 reliable might be a little bit of a stretch. That’s not because it’s plagued with endless common problems. Rather, a few of the issues can just be very serious.

Subaru EJ255 Common Problems Summary

The Subaru EJ255 is a solid overall engine. It offers impressive performance from the 2.5L turbo flat four, which comes with its own unique sounds. There’s also a lot of information and aftermarket support for the EJ255. The engine responds well to mods, but has its limits. If you intend to mod your Subaru 2.5L stick with a conservative tune or upgrade the internals.

We don’t think the number of problems with the EJ255 are concerning. It’s a reliable engine in that regard. However, turbo failures and internal problems with rings, ringlands, pistons, and rod bearings can be costly. The engines are also aging, so expect the normal wear and tear items like valve cover gaskets, coolant hoses, etc. Nonetheless, maintain your EJ255 well and chances are it will reward you with a fun, reliable experience.

What’s your experience with the Subaru EJ255? Are you considering one?

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Looking for more Subaru EJ or WRX content? Check out our awesome guides including the EJ255 vs EJ257 and WRX reliability and common problems.