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Subaru 2.5 engine: power and performance


Available in multiple configurations and versions, Subaru’s 2.5L flat-four engine has been a mainstay of the brand’s lineup for many years. We review its best aspects.

2.5 GT engine - Picture of Subaru

Of the major Japanese automakers, Subaru is the only one with a reputation for being a little unconventional. Standard all-wheel drive on most of their cars, unique styling, and a boxer engine help set them apart from the Toyotas of the world.

When it comes to those unique boxer engines, the heavyweight of the bunch is the 2.5-liter four-cylinder. Available across most of the lineup, the “EJ” and newer “FB” have been under the Subaru hood for 32 years.

Let’s see what the keys were to the success of this unorthodox engine design.

Subaru WRX 2020 - Image by Subarxu

Subaru 2.5L EJ Engine: Why start with a Boxer?

We start with the basics: all EJ series engines share a horizontal four-cylinder, 16-valve configuration with displacements from 1.5 to 2.5 liters. But why a boxer to begin with?

Carlos Benz (yes, of Mercedes-Benz fame) patented the four-cylinder engine in 1896, and Subaru introduced it to its lineup in 1971.

Motor Trend explains that the engine was configured to be in line with the transmission and had a lower center of gravity to help minimize body roll compared to inline-four and V-type engines, which have a higher center of gravity and tend to tilt laterally. lateral vibrations.

The design was also lighter and more compact, which is important for a young automotive company trying to get its feet on the ground.

2020 Subaru WRX STi - Picture of Subaru

EJ engines: naturally aspirated or turbocharged

As you would expect from an engine that has 30 years of history, the EJ can be available in a variety of configurations. There is a less complex single overhead camshaft (SOHC) design or a more efficient and powerful double overhead camshaft (DOHC) design.

DOHC engines are more difficult to maintain when it comes time to change the spark plug. That’s why these engines have platinum-tipped spark plugs, extending service intervals to 80,000 miles. You can have your EJ in naturally aspirated or turbocharged form.

All 1998 or later DOHC and SOHC EJ engines are interference engines, so if the timing belt fails, valve damage is likely. It is recommended to replace the timing belt every 60,000 miles to prevent this from happening.

We’ll focus specifically on the 2.5-liter engine, which was introduced in the Legacy 2.5GT and Outback in 1996. Turbocharging was introduced in the 2005 Legacy and the 2005 revision of the WRX.

Car and driver rated different from the 2.0-liter version of a 2006 WRX. The new horsepower and torque are available at lower rpm, eliminating much of the lifeless feel the WRX had before the turbo entered the room around 4,000 rpm.

The EJ25 will soon be discontinued, with the current WRX STI being the last model to receive it.

2013 Subaru WRX - Picture of Subaru

EJ25 Engine Problems and Known Issues

Subaru has an excellent reputation for reliability, but there are always issues to consider, and the EJ is no different. Some problems encountered with the EJ engine include a faulty fuel pump that could cause the engine to stall and an engine computer that has the potential to continue powering the ignition coil even after the engine is turned off.

FB25 engine: lighter = more efficiency The FB25 was introduced in 2011 with the Forester, and although the displacement of the EJ25 and FB25 is 2.5 liters, the FB is slightly larger, with 2,498 ci compared to 2,457. There are again non-turbo engines and turbo versions.

Subaru says the main motivation for the new engine was improved efficiency, claiming a 28% reduction in friction losses, with lighter pistons and connecting rods being the main contributors.

All of this adds up to just one additional mpg of range, but it’s actually a 5 percent increase, and that’s misleading because the FB engine was initially paired with older transmission designs.

With standard all-wheel drive, Subaru’s vehicle offerings will often have less range compared to a front-wheel drive competitor.

This new engine is also chain-driven (as opposed to the EJ’s belt), which is a stronger configuration that allows for a new block design with lower emissions. It also has variable valve timing to improve power and efficiency.

“Making these same EJ upgrades would have resulted in a much heavier engine.” Car and driver reports.

Jalopnik liked the boxer/AWD combination. “To Subaru’s credit, the Boxer/AWD formula is still brilliant,” they said. “While automakers are packing all the technology they can into their four-wheel-drive systems to make sure young families don’t drive off a cliff in their crossover, none of them will ever reach the low center of gravity. from a horizontally opposed engine.

FB25 Engine Problems and Known Issues

Some of the FB series engines consume oil and owners need to top up the oil every few thousand miles. Mechanic Youtuber Mr Subaru 1387 tells us that “this raises concerns about longevity” and that “as they wear down, oil consumption will increase.” This could cause deposits on the pistons, spark plugs, and oxygen sensors. The oil specification for this engine doesn’t help much, it is a very light 0W-20.

MDH Motors took apart a defective FB25 and discovered, “This engine was burning so much oil that it was damaging the catalytic converter and completely burning the exhaust valves.” To resolve this problem, Subaru has issued a technical service bulletin that replaces the piston rings after inspection, if they determine that the engine is using too much oil.

There was also a recall for engine valves that can fail, according to Consumer Reports in 2019. “Subaru is recalling certain Crosstrek, Forester and Ascent SUVs, as well as Impreza hatchbacks and sedans because they can suddenly lose power while driving, which could cause an accident,” he said. consumer reports. “A faulty part in the engine could allow oil to go places it shouldn’t. Pieces of the part could also separate and damage other engine components, which could cause a sudden loss of engine power.

Differences between EJ and FB engines

The EJ was phased out in the late 2010s due to limitations in its design, such as port fuel injection vs. newer direct injection in the FB engine.

At EngineBuilder, Nemesis Performance’s Justin Anning explains, “It’s a completely different design to the EJ, although it’s still an opposed four-cylinder. It features direct injection technology, a mechanical fuel pump and asymmetrical connecting rods.

Engine operating states: “Compared to the EJ25, the FB25 responds better at low speeds. Having identical power, it achieves lower rpm and higher torque at lower rpm. In addition, it consumes less fuel.

2020 Subaru Outback - Picture of Subaru

Should you buy a used Subaru with the FB25 or EJ25 engine?

We’ll use the Forrester as an example since it’s Subaru’s most popular model.

Autotrader gives important advice, “Those looking to spend a little more should upgrade to the fifth generation Forester, preferably a 2016 or newer, as these models do not suffer from the oil consumption issues that plagued some 2014 and 2015 models.”

Subaru offers certified vehicles that are subject to a 152-point inspection and a seven-year/100,000-mile powertrain warranty, which should give you some peace of mind about the longevity of your Subaru engine.

A Subaru offers many advantages over its competitors, and with an overall reputation for reliability and safety from standard all-wheel drive, you’ll be able to enjoy many trouble-free miles with your 2.5-liter Subaru engine, no matter what. the model you choose.

Images: Subaru


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