Subaru's EE20 engine was a 2.0-litre horizontally-opposed (or 'boxer') four-cylinder turbo-diesel engine. For Australia, the EE20 diesel engine was first offered in the Subaru BR Outback in 2009 and subsequently powered the Subaru SH Forester, SJ Forester and BS Outback. The EE20 diesel engine underwent substantial changes in 2014 to comply with Euro 6 emissions standards – these changes are discussed below and summarised under ‘Euro 6 changes’.
Please note that this article considers the EE20 engine as it was supplied in Australian-delivered vehicles. As such, it does not consider the Euro 4 emissions compliant EE20 engines that were available in Europe. Furthermore, specifications for other markets may differ from those in Australia.
The EE20 engine was manufactured on the same assembly line as Subaru's six-cylinder horizontally opposed petrol engines at its Oizumi factory.
The EE20 engine had an aluminium alloy block with 86.0 mm bores and an 86.0 mm stroke for a capacity of 1998 cc. For its Euro 4 and Euro 5 versions, the EE20 engine had a semi-closed block (i.e. the cylinders bores were attached to the outer case at the 12, 3, 6 and 9 o’clock positions) for greater rigidity around the head gasket. For the Euro 6 EE20 engine, however, an open deck design was adopted which eliminated the 12 and 6 o’clock supports.
For the EE20 engine, all five main bearings in the cylinder block had metal matrix composite journals (inserted during the cast process) for rigidity and due to their similar thermal expansion to the crankshaft. Furthermore, cooling slits between the cylinder bores provided water cooling channels.
For comparative purposes, dimensions of Subaru’s EE20, EJ20 and EZ30 engines are given in the table below.
Crankshaft, connecting rods and pistons
To withstand the high combustion pressures of a diesel engine, the crankshaft for the EE20 engine was subjected to a surface treatment for increased strength. Furthermore, the crankshaft journals were made from aluminium and cast iron due to the high pressure applied on both side of the cylinder block.
The forged connecting rods had fracture split bearings for the crank end and an asymmetrical profile which increased precision during assembly. The pistons had internal cooling channels, while oil jets in the crankcase sprayed the underside of the pistons.
The EE20 engine had an aluminium alloy cylinder head that was 17 mm thinner than the EJ20 engine. Furthermore, the intake ports and the diameter of the intake valves were designed to create a swirling effect for the air as it entered the combustion chamber.
The EE20 engine had double overhead camshafts (DOHC) per cylinder bank that were driven by a chain and gear with a speed-reducing gear. The four valves per cylinder (two intake and two exhaust) were actuated by pivot-type roller rocker arms.
The EE20 engines have IHI turbochargers with variable nozzle turbines (VNTs). Generally, VNTs use movable vanes in the turbine housing to adjust the air-flow to the turbine to realise comparable exhaust gas velocity and back pressure throughout the engine’s rev range. To enhance torque at engine speeds below 1800 rpm, the nozzle vanes would close to narrow the air path and increase the speed of the air flow. At higher engine speeds, however, the vanes would open to reduce airflow resistance and improve fuel consumption.
Initially, the turbocharger was positioned under the engine. For the Euro 6 EE20 engine, it is understood that the turbocharger was relocated to the bottom right of the engine. It is understood that the maximum turbine speed for the IHI turbochargers used in the EE20 engine is 190,000 rpm.
Injection and combustion
The Euro 4 and Euro 5 EE20 diesel engines had a Denso common-rail injection system with eight-hole, solenoid-type injectors that achieved an injection pressure of 180 MPa. For the Euro 6 EE20 engine, however, injection pressure was increased to 200 MPa. For the EE20 engine, the injectors were positioned at an almost 90 degree angle to the cylinder and were 40-50 mm shorter than those used in inline four-cylinder diesel engines.
The Euro 5 and Euro 6 EE20 engines are understood to have ceramic-type glow plugs.
EGR and DPF
The EE20 diesel engine had a water-cooled exhaust gas recirculation (EGR) system which recirculated exhaust gases to the intake to lower combustion temperatures and reduce NOx emissions.
The Euro 5 and Euro 6 EE20 engines had a closed-loop diesel particulate filter (DPF); both the oxidation catalyst and DPF were positioned next to the turbocharger to utilise the heat of the exhaust air.
The alternator for the EE20 diesel engine had a voltage charging control system which, to reduce the alternator’s load on the engine, reduced the charging voltage when the vehicle was idling or being driven at a constant speed and increased voltage at low speeds.
Euro 6 changes
The Euro 6 emissions compliant EE20 diesel engine was introduced in the Subaru BS Outback in 2014 and the Subaru SJ.II Forester in 2015. Relative to the Euro 5 version, changes for the Euro 6 EE20 engine included:
- An open deck cylinder block;
- An increase in piston crown capacity;
- A new piston skirt coating was introduced to reduce friction;
- A reduction in the compression ratio to 15.2:1 to lower combustion temperature and reduce NOx emissions;
- A fourth generation common rail injection system was introduced for higher injection pressure (200 MPa, previously 180 MPa) and a finer fuel spray;
- Each diesel injector had an integrated driver unit to reduce fuel leak volume, fuel pump load and improve fuel economy;
- A low-friction timing chain was introduced to drive the fuel pump (previously gear-driven) for quieter operation;
- The glow plugs were revised to improve pre-heating temperature at start-up and increase after-glow time;
- Oil jets were added to the timing chain drive;
- A low-pressure EGR circuit was introduced to increase the EGR rate, while the high-pressure EGR circuit was ‘optimised’;
- The turbocharger repositioned at the bottom right of the engine (previously under the engine) and improved vane control was achieved;
- The diesel particulate filter (DPF) substrate specifications were revised and regeneration performance enhanced. The type and amount of precious metals in the oxidation catalyser and DPF catalyst were also revised;
- The number of idlers used in the auxiliary belt system was reduced;
- A more precise sensor measured battery current, voltage and temperature; and,
- The rear flange and bracket material, exhaust pipe and end plate material were changed for rust prevention.
Just in case you've missed the reviews about this new engine, make no mistake – this is seen as one of the best diesel engines in the world. It's quiet, smooth, refined and powerful – but most importantly it's class-leading in terms of emissions and economy.
2010 Subaru Outback Diesel Problems
Subaru Outback diesel problems don't seem to be too frequent or too common. And that's probably in line with the brand's overall reputation for reliable engineering.
While results will vary and the big variable is always how well the car has been maintained, what I can tell you is a Subaru is capable of going 300,000 miles. And if you are a regular maintenance type of owner you should expect to get that type of mileage out of it.
Subaru EE engine (diesel)
This 2.0L DOHC engine, designated the EE20, has an output of 110 kW (150 PS; 150 hp) at 3600 rpm and develops 350 N⋅m (36 kg⋅m; 260 lb⋅ft) of torque at 1800 rpm, with a redline of 4750 rpm.
Subaru 2.5-L Turbo Four Cylinder
Owners of 2009-14 Subaru Impreza WRX and WRX STI models have launched a class-action lawsuit, alleging the pistons and PCV (positive crankcase ventilation) systems in the high-performance 2.5-L turbocharged engines may overheat or malfunction, requiring a king's ransom in repairs.
A number of Subaru models are affected, however the most common failures include the 2.5 Liter SOHC engine used in the late 1999-2004, Forester, Impreza, Outback and Legacy. Signs and symptoms of engine head gasket failure include: Engine overheating.
- Weak windsheilds in the Subaru Outback. ...
- Damaged oxygen sensors. ...
- Faulty airbag inflators. ...
- Headlight burning out on the Subaru Outback. ...
- Oil leaks. ...
- Cooling failures. ...
- Transmission Prolblems with the Subaru Outback. ...
- Vibration while accelerating.
The Outback's sole engine choice is a naturally aspirated 2.5-litre petrol mated to a CVT gearbox. Subaru's decision to drop its 2.0-litre diesel engine is almost certainly due to it not meeting the standards of the WLTP (Worldwide Harmonised Light Vehicles Test Procedure) regulations, which come into force next month.
Subaru engines typically last 200,000 miles before needing significant maintenance or repairs, with the exception of the top model. According to Forbes, the Subaru Forester is one of the ten most likely models to reach over 250,000 miles on a single charge.
- Keep It Clean. Keeping your Subaru clean is a great way to protect it against rust, dirt, and other unwanted buildup both inside and outside the vehicle. ...
- Follow the Service Schedule. ...
- Take It Easy on the Engine. ...
- Check the Levels. ...
- Let the Engine Warm Up. ...
- Professional Assistance.
Most Subaru models can be trusted to run, without major issue, for about 150,000 to 200,000 miles. That's as long as owners perform routine maintenance and care of those vehicles.
Overall, Toyotas are more reliable than Subarus. They have consistently won more distinctions and awards across all models and have higher scores with both Consumer Reports and J.D. Power.
These problems included oil burning, oil starvation, and head gasket issues. These problems were not caused by heavy mileage and abuse, but because of the engine's design and its poor engineering. Also, it had plenty of quality issues. Now let's discuss these Subaru engine problems one by one.
With a total power output of 326 hp, the Subaru WRX STi Type UK takes joint first place. It's a 5 door AWD Fastback with 5 seats and a front-mounted 2.5L Flat 4 Turbo Gasoline engine. See all the tech specs here. It is also joint 1st in The Highest Torque Subarus Ever.
In 2019, Subaru recalled more than 450,000 of its models in the U.S. to address engine computer issues. According to reports, the computer unit was incorrectly programmed, causing it to continue to power the ignition coil even after the motor had been shut off.
Subaru's decision to drop its 2.0-litre diesel engine is almost certainly due to it not meeting the standards of the WLTP (Worldwide Harmonised Light Vehicles Test Procedure) regulations, which come into force next month.
H6 is a fantastic engine, I specifically went with it over the EJ25 when we got our OBW due to feedback on it's reliability. The "common" issues with it are rather benign and easy to fix. The drive belt pulley bearings are common to go out, but it's like a 15 minute fix and very easy and not a big deal.
Is The Subaru Boxer Engine Reliable? Boxer engines are not entirely reliable. They lack reliability, which means they have a bad reputation. In the summer of 2010, Subaru had to amend its warranty term for its powertrain because of these issues.
Is the Subaru EZ36 flat-6 engine reliable? Yes, we believe the EZ36 earns average to above average marks for reliability. The engine doesn't have any serious design flaws or issues. Still, no engine is perfect and that also applies to the 3.6L flat-6 Subaru engine.