When you’re buying a car, you know that the engine is the heart of the machine. But what are the details behind the Subaru 2.5 engine? By having a better understanding of what’s under your vehicle’s hood, you have a better idea of what your vehicle can do for you.
What are the specs of a Subaru 2.5 engine?
The Subaru 2.5 engine is a 16-valve flat-four boxer naturally-aspirated and turbocharged engine with a 2.457L displacement. Depending on the year, make and model it appears in, the engine’s HP ranges from 155 to 172.6 and 140 to 170 lb.-ft.
But what’s going on with this engine beyond simple specifications? What kind of questions do owners have? We’ve gathered information from all over the internet, including the NHTSA website and Vehicle History’s extensive database, so you can find everything you need to know right here in one easy location.
History of the Subaru 2.5 Engine
The Subaru 2.5 engine, including a range of different engines otherwise known as Subaru’s EJ25 series, the EJ25D, EJ251, EJ252, EJ253, EJ254, EJ255, EJ257 and EJ259, were introduced in several trims of the Legacy from 1994 to 1996, including the GT, LSi and Legacy Outback.
When developing the Subaru 2.5 engine, the manufacturer went away from the typical inline-four or V-based engines for a flat-four design, which Subaru refers to as a “boxer” engine. It is so named because the pistons are positions 180 degrees apart, so they push toward each other, like boxers punching.
This unique approach to engine design provides several benefits. The flat design allows direct input from the engine and transmission which improves fuel efficiency, while the lower vibration caused by the opposite pistons, reducing the need for additional components that are found in many V-based engines to compensate for this.
The lower center of gravity provides better performance and handling. This same feature allows the engine to drop below the passenger compartment in an accident rather than into the passenger compartment, reducing injuries.
As time has progressed, the EJ25D was replaced by the EJ254 and EJ257, which are dual overhead cams models, which were used in a limited amount due to the flat-four’s complex architecture making changing plugs difficult. Subaru handled the issue by using extended-life platinum spark plugs for less-frequent maintenance.
Due to the architecture, many more Subarus received the single overhead cam configuration, starting with the EJ251. The EJ252 was designed specifically for California emission laws, while the EJ253 dropped its horsepower by 5 HP and exchanged a MAP sensor for a MAF sensor.
Which Models Have a Subaru 2.5 Engine?
There are several Subaru models that feature a 2.5 engine. The start of the 2.5 engine was the Legacy, including the EJ25D engine from 1994-1999, EJ251 from 1999-2004, EJ252 from 2000-2002, EJ253 from 2009-2012, EJ255 from 2005-2012, EJ257 from 2005-2006 and the EJ259 in 2004.
The Outback has also seen a number of these engines, starting with the EJ25D from 1996-1999, the EJ251 from 2000-2004, the EJ252 from 2000-2002, the EJ253 from 2003-20012 and the EJ255 from 2005-2020. The Baja used the EJ251 from 2003-2005 and the EJ253 from 2005 onward, with the Baja Turbo using the EJ255 from 2004-2006.
The Forester used the EJ25D from 1997 to 1998, then switched to the EJ251 from 1999-2004, the EJ253 in 1999 and again from 2005-2010, the EJ254 from 1998-2002 in the T25 version and from 2004-2020, the EJ255 from 2004-2013 and the EJ257 from 2004-2005 in the XT trim.
The Impreza only used the EJ25D engine for one year, in 1998, then switched to the EJ251 from 1998-2003, the EJ253 in 1999 and again from 2004-2011, the EJ255 from 2006-2014 and finally the EJ2057 from 2004-2018.
People Also Ask
Are Subaru 2.5 Engines Reliable?
Though Subarus are known for reliability, their 2.5L engine has some issues it shares with the 2.0 engine. It tends to have issues with head gasket and crankshaft oil / seal oil leakage, as well as a knocking noise that comes from the fourth cylinder, which runs the hottest and cools most poorly out of all cylinders in the engine.
What is the Subaru 2.5 I Engine?
The Subaru 2.5 engine is a boxer engine, which means that rather than the pistons moving in and out at an angle, the pistons move at 180 degrees from each other, like boxers throwing punches at each other, one then the other. This creates a smoother ride and better handling when the vehicle is underway.
What are the Subaru 2.5 Engine Specs?
The Subaru 2.5 engine features a 99.5 mm bore and a 79 mm stroke. The 1996 engine has a 9.5 compression ratio, which was upgraded to a 9.7 ratio from 1997-1999 and finally a 10.0 ratio from 2000 on. It’s capable of delivering between 155-170 HP and 140-176 lb.-ft. of torque.
How Long Do Subaru 2.5 Engines Last?
Many owner reviews mention the Subaru 2.5 engine providing many years and miles of dependable service. These include over ten years of reliable service and over 200,000 miles with no serious issues with the vehicles.
Are Subaru 2.5 Engines Interference Engines?
All Subaru 2.5 engines are interference engines, but what does that mean? An interference engine provides more horsepower with better fuel economy because the pistons and valves could interfere with each other during operation if specific timing is not maintained. If the timing belt breaks, it can cause serious damage.
Buying a Used Car? Make Sure You Do it Safely
Start by checking its Vehicle History! We’ve partnered with brands and websites like KBB, the NHTSA, and more to provide you with a no-cost tool to use on the go, so you can make a smart choice fast.
