Home TroubleshootingEngine Subaru 2.5 Engine – Everything You Need To Know

Subaru 2.5 Engine – Everything You Need To Know

by Kelvin Yates

Are you on the market for a new or used car and you are looking for a Subaru with a 2.5 engine? If this is the case and you want to further investigate the matter and learn more about the Subaru 2.5 engine, then you are at the right place because there will be a lot to cover when it comes to this engine.

Performing proper research on the vehicle before you even think of purchasing it is key. You need to familiarize yourself with the car before you buy it. Buying a car is not as simple as most people think since it requires quite a bit of experience and knowledge to find a car that is really good and will deliver excellent performance for your budget.

That’s why you need to learn more about Subaru and their engines. Learning how these engines work and their possible problems would be a lifesaver for you because you will have the right picture and will know what you can expect out of them. You will not be surprised as many other Subaru owners are. And frankly, the Subaru 2.5 engine is full of surprises. You just never know what you are going to get in yours.

But we are going to help you out learn at least the basics. First, we are going to cover the Subaru 2.5 engine and its basics. Then we will learn the pros and cons of the Subaru boxer engine design and then we will learn the specs in which this engine is offered. Later we will focus on the problems of this engine, the reliability of this engine, and whether you should get it. So, let’s get into it.

Boxer Engine

So, what is the Subaru 2.5 engine? This engine is an engine produced by the Japanese car manufacturer Subaru. The engine is also known as the EJ engine.

The EJ engine is a whole series of flat-four engines that are rated from 1.5L up to 2.5L of displacement. But in this article, we will stick to the 2.5 since this engine is the most important for us right now.

And frankly, this series of engines is something that almost everyone connects Subaru with. They have built a big reputation around these engines and they don’t even think of stepping back from this design.

Subaru 2.5 Engine

The EJ series was first introduced back in 1988 and is still produced to this day as we mentioned. The EJ series is a boxer engine layout. But what does a boxer mean?

The term boxer engine refers to the engine layout. Meaning that these engines are not vertically installed, nor that they are turned at an angle like in the V8 configuration. But what boxer engines implement is a horizontal piston layout.

Meaning that the crankshaft is in the dead center and the pistons are laid out horizontally. When the engine works, it looks like two boxers are having a sparring match. It’s that cool. But these engines also have downsides that are worth covering and more on that we will learn in the following chapters where we will learn the pros and cons of the Subaru 2.5 boxer design.

Boxer Engine Pros And Cons

Now before we dive into the Subaru 2.5 engine. Let’s first discuss the pros and cons of this engine design. This is quite useful to know because everything revolves around the pros and cons.

Here you will see if this engine is the right one for your future vehicle or not. This is because flat engines are not like other types of engines and are a little bit more complex to run. But more on that in the following two chapters where we will explain this in detail.

Pros Of The Boxer Engine

Now let’s first learn the pros of the Subaru 2.5 engine. The main pros of this engine are its unique design. The engine is laid up horizontally instead of vertically and this makes it quite unique from other engine designs. If you are one of those guys who want to have something special, this engine is the right one for you.

Another thing is the overall stability of the vehicle. The boxer engine sits low in the engine compartment and this makes sure that you have a low center of gravity in your vehicle. A lower center of gravity means greater stability on the road. The car will handle much better than some cars with a V8 engine or inline engine design.

Having the engine sitting low will also improve the balance of the car. If you drive a Subaru you will notice how there are low or no vibrations inside of the cabin. This is all made possible because of this engine design that is really good and delivers no vibrations at all.

Another positive thing about the boxer engine is the safety aspect. The engine sits low and in case of an accident, it will help in protecting you. And that’s about with the pros of the Subaru 2.5 engine. Now let’s learn the cons of this engine.

Cons Of The Boxer Engine

Subaru 2.5 Engine

Now let’s learn the cons of the Subaru 2.5 engine. And it is worth that there are a few of these cons that can change your mind.

The biggest con of the boxer engine is the maintenance. This engine is quite difficult to maintain and also quite expensive. So, why is this the case? Let’s elaborate.

This engine is laid up horizontally, meaning that it covers the space from one side to the other side of the engine bay. There is just not a lot of place for wrenching. This makes replacing even common parts like spark plugs quite difficult. For some more complex work, the whole engine needs to come off and this is quite expensive to pull off.

In addition to this, these engines are also a bit more complex than your regular inline engine and require more knowledge and people who understand these engines to work on them. This means that you will often be needed to take your Subaru to the dealership for any work to be done properly. And, there are not a lot of independent Subaru shops across the country.

Also, this engine design also has some problems that are in its DNA. And no matter what Subaru 2.5 engine you get, there still be these problems. But more on that in a bit after we cover the specs of the EJ engine. We will focus on the 2.5L only since this article is all about it.

2.5 Subaru Engine Specs

As we speak about the Subaru 2.5 engine, our focus would be on the EJ25 engine and its variations. EJ means that it belongs to the EJ family of engines and the 25 is referring to the displacement of 2.5L.

It is worth noting that there are a number of engines under this name. The earliest out of the bunch is the EJ25D. This engine was produced from 1994 up until 1999 and was included with the Impreza, Legacy, and Forester models. It was a naturally aspirated engine that produced about 158hp and 220lb-ft of torque.

Then there were some variations through the years. Namely, the EJ251 was a big improvement in comparison to the basic engine and this engine implemented a single overhead camshaft design. It produced a bit more power, 165hp to be more exact.

Then there was the EJ255 which is the most powerful engine that Subaru offered. This is a high-performance engine that has a power output rated between 207 and 261hp. It was included in the high-performance applications.

In present models, the EJ is not in use anymore and was replaced with the FB series of engines. Namely, the FB25B and the FB25D. The D model is the latest model and is included in all 2020+ models. These engines are naturally aspirated and produce 170hp for the B model and 182hp for the D model.

So, if you want to get a new Subaru, then it’s probably going to be equipped with the FB25D. But what are the Applications of the Subaru 2.5 engine? Let’s elaborate in the following chapter.

Subaru 2.5 Engine Applications

Now let’s learn more about the Subaru 2.5 engine applications. In which Subarus you can find these engines to begin with?

Luckily for you, this engine is used among a lot of Subaru models and you shouldn’t be desperate that your favorite Subaru doesn’t have one.

The important thing is that this engine is quite versatile and can be used in a number of applications. But not in all of the Subarus out there.

For example, the most modern F25B is not used in the Impreza, which is a bummer. But that’s how things go sometimes. The latest 2.5 engine is only used in the Legacy, Outback, Forester, and Crosstrek.

The EJ on the other hand can be found in the models that we mentioned above, as well as the Impreza, the Impreza WRX, and the Subaru Baja which was discontinued.

What is strange though is that this engine can also be found in the Saab 9-2x. The only non-Subaru model that ran this engine. Overall, that’s everything you need to know when it comes to the applications of the Subaru 2.5 engine.

Remember, the EJ is before 2020 and the FB is used after 2020. The FB is the most modern engine out there made by Subaru and also quite a bit more reliable than the EJ engines. But now we are entering new territory. And those are the Subaru 2.5 engine problems.

But don’t worry, we are not done with this Subaru engine. In the following chapters, we are going to cover precisely that and focus on the main problems of the Subaru 2.5 engine problems.

Subaru 2.5 Engine Problems

Now we come to the important bit when it comes to the Subaru 2.5 engine and that is the problems this engine has. Knowing the problems of this engine will help you out immensely when it comes to deciding on whether you should opt for a Subaru or maybe go for another car.

And unfortunately, the Boxer engine has its flaws that are worth covering. Some of these problems are major while some of them are only minor. But we are going to cover them anyway since we want you to have the best and get a car that you will really love and enjoy. So, if you want to learn more, follow along.

Subaru 2.5 Engine, Problems #1. Head Gasket Problems

The biggest problem the EJ Subaru 2.5 engine has is the problem with the head gaskets. They just love to fail on these engines.

More of these failures are attributed to poor gasket materials. But also some of them are attributed to the engine design. Usually, the gaskets lay flat or at an angle. But in boxer engines, the gaskets are vertical. So, gravitation doesn’t do any benefit to them.

Meaning that it is quite more probable for them to leak since they are installed in this way. On many of these engines, the coolant leaks from the sides of the engine since the gaskets are tiny, and as they degrade, the coolant escapes and burns off.

This problem often makes this engine very unreliable since a lot of damage can be done to it especially if the engine has been running like this for a while and hasn’t been checked by a mechanic.

Having an engine running with a problem like this will guarantee the expensive repairs that will come after. So, you need to be aware of this problem and make sure that the Subaru 2.5 engine you purchase is actually good. It is better to be safe than sorry later.

The possible outcomes from a blown head gasket can lead to the mixing of coolant and oil. And this mixture is not good since the bearings inside of the engine will get toast if you run your car like this. This means that the whole engine will have to be either rebuilt or replaced. So, beware of this problem. Now let’s move to the other problems of the Subaru 2.5 engine.

Subaru 2.5 Engine, Problems #2. Oil Consumption

The second biggest problem with the Subaru 2.5 engine is the oil consumption from which this engine suffers from. Yup, that’s right. Subaru engines drink more oil than other engines.

The EJ engine has a specific problem with its oil rings that often fail after a lot of miles and are starting to let some of the oil inside of the combustion chamber.

As the oil enters the combustion chamber it starts to burn. When the oil is burning you will notice how the car will start to lose oil pressure and the oil light will come on.

This should not be ignored and you should always check the oil level. It is likely that the oil is getting low and it needs to be topped off. When you have a car that likes to burn more oil than it should, it is useful to carry a quart of oil in the trunk and top off the oil whenever it gets low.

Do all Subarus have this problem? Pretty much. More precisely engines that have reached 100,000 miles or so. This is the point when the engines are starting to show their downsides but on Subarus, this happens more often and people are asking themselves if Subarus is good as a second-hand option. Because they are far more prone to problems than other cars.

They are good, but what is most important is the maintenance that this Subaru 2.5 engine had during its lifespan. If this engine was maintained, then you shouldn’t worry much about it. Nevertheless, let’s move on to the following problem.

Subaru 2.5 Engine, Problems #3. Oil Starvation

Oil starvation is another problem that this engine has. Namely, this is a problem with the engine design itself. These engines suffer from a lack of lubrication because they are designed this way and it is often difficult to get properly lubed.

Especially when the engine suffers also from oil consumption. And if you leave it like this for quite a bit of time on low oil, the oil starvation problems are even more serious.

The biggest hit will take the rod bearings and the rods will start knocking. The rod bearings simply do not want to run on low or no oil. If they do, engine damage is imminent.

This means that sooner or later, the engine will start to wear down quicker and basically you can thrash your engine. A new engine will be needed. Or a rebuild of the existing engine.

That’s why you need to be aware of this problem and try not to leave your Subaru 2.5 engine running low on oil at any cost.

Subaru 2.5 Engine, Problems #4. Overheating

Overheating is another common problem with the Subaru 2.5 engine. This can be attributed to a number of reasons, including a malfunctioning radiator, a faulty water pump, or even a clogged coolant system. However, the head gasket problem mentioned earlier can also lead to overheating.

When the head gasket leaks, it can cause coolant to mix with oil or escape from the engine, leading to the engine overheating. This overheating can cause further damage to the engine and other components.

If you notice your Subaru 2.5 engine running hotter than normal, it is advisable to pull over as soon as possible and check the coolant level. If it’s low, there might be a leak somewhere, and it’s recommended to get it checked by a professional.

Subaru 2.5 Engine, Problems #5. Spark Plug Failure

The spark plugs in the Subaru 2.5 engine are prone to failure. This is due to the fact that the spark plugs in this engine are located in a somewhat awkward position which makes them prone to oil and dirt accumulation. Over time, this accumulation can lead to the failure of the spark plugs.

If the spark plugs fail, the engine will misfire, leading to poor performance and fuel economy. Additionally, a misfiring engine can lead to increased emissions, which can cause your vehicle to fail an emissions test. Therefore, it is essential to regularly check and replace the spark plugs as part of your routine maintenance.

Subaru 2.5 Engine, Problems #6. Timing Belt Failure

The timing belt is a critical component of the Subaru 2.5 engine as it ensures that the engine’s valves open and close at the correct times. However, the timing belt on this engine is known to fail prematurely, which can lead to catastrophic engine damage.

If the timing belt breaks while the engine is running, it can cause the valves to collide with the pistons, resulting in bent valves and damaged pistons. This can lead to a very expensive repair bill as it often requires a complete engine rebuild or replacement.

Therefore, it is crucial to replace the timing belt at the recommended intervals specified in your vehicle’s owner’s manual.

Subaru 2.5 Engine, Problems #7. Turbocharger Failure

For the turbocharged versions of the Subaru 2.5 engine, turbocharger failure is a common issue. The turbocharger increases the engine’s power by forcing more air into the combustion chamber. However, the turbocharger in this engine is known to fail, leading to a loss of power and increased exhaust emissions.

The failure of the turbocharger can be attributed to several factors, including oil starvation, excessive exhaust temperatures, or even manufacturing defects. Therefore, it is essential to regularly check the turbocharger and the associated components and replace them as needed.

Subaru 2.5 Engine, Problems #8. Throttle Body Issues

The throttle body is a critical component of the Subaru 2.5 engine as it controls the amount of air that enters the engine. However, this engine is known to have issues with the throttle body, such as a faulty throttle position sensor or a clogged throttle body. These issues can lead to poor engine performance, stalling, and even a check engine light.

It is recommended to regularly clean the throttle body and replace the throttle position sensor as part of your routine maintenance to avoid these issues.

Subaru 2.5 Engine, Problems #9. Ignition Coil Failure

The ignition coil is responsible for converting the battery’s voltage into a higher voltage needed to ignite the fuel in the combustion chamber. However, the ignition coil in the Subaru 2.5 engine is known to fail, leading to misfires, poor performance, and a check engine light.

Regularly checking the ignition coil and replacing it as needed can help avoid these issues.

Subaru 2.5 Engine, Problems #10. PCV Valve Failure

The PCV (Positive Crankcase Ventilation) valve is a one-way valve that helps remove combustion gases from the engine’s crankcase. However, the PCV valve in the Subaru 2.5 engine is known to fail, leading to increased oil consumption, a rough idle, and even engine misfires.

Regularly checking the PCV valve and replacing it as needed can help avoid these issues.

In conclusion, while the Subaru 2.5 engine is known for its durability and performance, it does have its share of common problems. Regular maintenance and timely replacement of faulty components can help prolong the life of your Subaru 2.5 engine and ensure it continues to perform at its best.

Subaru Boxer Engine Reliability

So, what is the reliability score of the Subaru 2.5 engine? Is this a reliable engine or maybe not? Well, the answer really depends.

The thing with Subaru engines is that they are more prone to problems because of their design in general. This might be a downside. But they also have a ton of upsides that make sure that you turn into a Subaru fan and never look at something else.

The overall reliability of this engine is about 3.5 out of 5 stars. I think that this is a decent grade and most people will agree with me on this.

When these engines are in relatively good condition they are one of the best out there. But when they are not loved that much by their owners. They will show you their bad side and make you regret that you purchased one.

So, should you get a Subaru 2.5 engine? Yes, or no? That’s what we are going to cover in the following chapter where we will elaborate more on this question and try to deliver you a sincere answer that will make your purchasing decision a lot simpler and easier to make.

Are Subarus Reliable

So, should you buy the Subaru 2.5 engine? The answer is yes, you should buy it. But you also need to be aware of what you are getting yourself into. Knowing the downsides of the engine will mean a lot for you since you will be prepared for possible problems that will often know to happen as the problem with the head gaskets, and the problem with the oil which is known to burn in the cylinders.

All these issues have their own level of difficulty and will require some money to get sorted. You just cannot expect to sort them out with a few pennies.

They will require extensive work to get them sorted. This is because the engine sits very low and is really tight against the engine bay walls. So, the space to work on the engine is very small and most of the common work needed will require more time and money invested to get things sorted.

Also, there are few Subaru independent shops everywhere across the states. So, you will have to rely on the dealership for most of the issues that you will come across. And as we know, dealerships are quite expensive, and fixing the car at their place will cost you a good penny. You will need to become your own mechanic if you want to get your expenses to the minimum.

In addition to this, you should try to find a relatively low mileage example. Stay away from higher mileage cars since most of them are not that good. Or if it’s a higher mileage car. Make sure that it is properly maintained and loved.

Facts about the Subaru 2.5 Engine:

  1. The Subaru 2.5 engine is a 16-valve flat-four boxer naturally-aspirated and turbocharged engine with a 2.457L displacement.
  2. The engine’s horsepower ranges from 155 to 172.6, and 140 to 170 lb.-ft., depending on the year, make, and model it appears in.
  3. The Subaru 2.5 engine was introduced in several trims of the Legacy from 1994 to 1996, including the GT, LSi, and Legacy Outback.
  4. The flat-four design of the Subaru 2.5 engine allows direct input from the engine and transmission, improving fuel efficiency and handling.
  5. The lower center of gravity of the engine provides better performance and handling, and it drops below the passenger compartment in an accident, reducing injuries.
  6. The EJ25D was replaced by the EJ254 and EJ257, which are dual overhead cam models used in a limited amount due to the flat-four’s complex architecture making changing plugs difficult.
  7. Many more Subarus received the single overhead cam configuration, starting with the EJ251.
  8. Several Subaru models feature a 2.5 engine, including Legacy, Outback, Baja, Forester, and Impreza.
  9. Subaru 2.5 engines have issues with the head gasket and crankshaft oil/seal oil leakage, as well as a knocking noise that comes from the fourth cylinder.
  10. All Subaru 2.5 engines are interference engines, which means that if the timing belt breaks, it can cause serious damage.

Subaru 2.5 Engine: In Conclusion…

In this article, we have covered quite a bit when it comes to the Subaru 2.5 engine. First, we learned what is the boxer engine and the pros and cons of this engine design. There are a few of them and they are worth your attention.

Then we covered the 2.5 engine specs and also the applications in which this engine was included. And frankly, most of the Subarus include this engine.

Then we have learned the problems of this engine and as we can recall, there are a few of them. Namely, head gasket issues, oil consumption, and oil starvation problems. Lastly, we learned if purchasing one for you is a good idea or maybe not.

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