Subaru EE20Z Specifications
| Engine Model: Subaru EE20Z |
| Engine Type: 4-cycle 4-cylinder DOHC 16-valve turbocharged liquid-cooled diesel |
| Total Displacement: 121.9 cu.in (1.99 L) |
| Rated Engine Power: 147 Hp (108 kW) at 3600 rpm |
| Fuel System Type: Common-rail direct injection |
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The Subaru EE20Z is a 2.0-liter,
horizontally-opposed (flat-four), dual overhead camshaft (DOHC),
16-valve, turbocharged common-rail diesel engine. It represents a
landmark achievement for Subaru as their first and only mass-produced
boxer diesel engine, developed in the late 2000s to meet European demand
for fuel-efficient, high-torque powertrains while retaining the brand's
signature low-center-of-gravity driving dynamics. The EE20Z features an
advanced common-rail direct injection system, a variable geometry
turbocharger (VGT), and a chain-driven dual overhead camshaft valvetrain
per bank.
Its horizontally opposed layout provides inherent smoothness and
packaging benefits but presented significant engineering challenges for
diesel combustion and durability, leading to a uniquely robust design.
This engine is renowned for its strong low-end and mid-range torque,
exceptional refinement for a diesel, and impressive fuel economy.
However, it is also known for its complexity and susceptibility to
serious issues if maintenance is neglected, particularly concerning its
timing chain system and fuel injection components. The EE20Z is a
technologically ambitious and characterful engine that remains a unique
curiosity in automotive history.
Engine Family / Model: Subaru EE series (Boxer Diesel), Model EE20Z
(Turbocharged Common-Rail).
Engine Type: Horizontally-opposed four-cylinder (flat-four, boxer),
longitudinally front-mounted, four-stroke cycle, water-cooled,
turbocharged and intercooled diesel engine.
Fuel Management: Common-rail direct injection (DENSO system, 3rd
generation with piezoelectric injectors). Aspiration: Forced induction
via a variable geometry turbocharger (VGT) and a front-mounted
air-to-air intercooler.
Bore: 86.0 mm / 3.386 inches. Stroke: 86.0 mm / 3.386 inches.
Displacement: 1,998 cc / 121.9 cubic inches.
Compression Ratio: 16.5 : 1 (relatively high for a modern common-rail
diesel).
Firing Order: 1-3-2-4. (Cylinders: Left bank 1-2, Right bank 3-4. Front
cylinders are 1 and 3).
Rotation Direction (from front/crank pulley): Clockwise.
Maximum Power Output (EC): 108 kW (147 Hp) at 3,600 rpm.
Maximum Torque: 350 Nm (258 lb-ft) at 1,800-2,400 rpm. Idle Speed:
750-850 rpm.
Fuel System Pressure: Up to 1,800 bar (26,107 psi).
Fuel Requirement: Ultra-low sulfur diesel (EN 590).
Emissions Compliance: Euro 5 standard, utilizing a Diesel Oxidation
Catalyst (DOC) and a Diesel Particulate Filter (DPF). Some markets also
used a Selective Catalytic Reduction (SCR/AdBlue) system.
Construction: Cast iron, with a deep-skirt, closed-deck design. This is
an exceptionally rigid and strong block to withstand the high cylinder
pressures of diesel combustion (peak 180 bar). The boxer layout requires
a split-case design for assembly.
Cylinder Bores: Integral (parent bore) in the iron casting, treated for
durability.
Crankshaft: Forged steel, supported by five main bearings. The
crankshaft is specific to the boxer layout, with crankpins shared by
opposing pistons.
Main Bearings: Steel-backed, aluminum alloy shell bearings.
Pistons: aluminum alloy with a sophisticated re-entrant combustion bowl
and anodized top ring land for extreme heat and pressure resistance.
Features cooling galleries fed by oil jets.
Connecting Rods: Forged steel, fracture-split big end caps.
Balance: No external balance shafts are required; the opposed-piston
layout inherently cancels primary vibrations.
Construction: aluminum alloy, one per bank. Feature integrated exhaust
manifolds within the head casting to improve warm-up and packaging.
Valve Arrangement: Dual Overhead Camshafts (DOHC) per bank (total of
four camshafts), driven by a complex single-stage duplex timing chain
system. Four valves per cylinder (16-valve total).
Valvetrain: Roller rocker arms actuated by the camshafts.
Combustion Chamber: Formed primarily in the piston crown, with a flat
cylinder head face (similar to a Heron-type head). Valve Seat Angle: 45
deg.
Valve Material: Intake valves are standard steel; exhaust valves feature
sodium-filled stems for enhanced heat dissipation.
Valve Clearance: Mechanical adjustment via shims located under bucket
followers. Clearance (Cold): Intake: 0.20-0.30 mm (0.008-0.012 in).
Exhaust: 0.30-0.40 mm (0.012-0.016 in). Requires specialized procedure
for access.
Camshaft Drive: Single, central duplex roller timing chain driving a
jackshaft, which then drives each bank's camshafts via smaller chains.
This system is known for potential issues with chain stretch, tensioner
failure, and guide wear.
Injection System: DENSO 3rd Generation Common-Rail with piezoelectric
injectors. These injectors allow for extremely fast and precise multiple
injection events per cycle (pilot, main, post).
High-Pressure Pump: Camshaft-driven, single-piston radial pump capable
of generating up to 1,800 bar pressure. Common Rail: A high-pressure
accumulator rail supplying fuel to all injectors.
Turbocharger: Variable Geometry Turbocharger (VGT) with an electronic
actuator, optimized for quick low-end response and sustained boost.
Intercooler: Front-mounted air-to-air intercooler.
Glow Plugs: Fast-acting ceramic glow plugs for cold starting, controlled
by a dedicated module.
Type: Full-pressure, force-fed wet-sump system with piston cooling jets
and an oil cooler.
Oil Pump: Trochoid-type (internal gear), chain-driven from the
crankshaft.
Oil Filter: Cartridge-type paper element.
Oil Cooler: Engine oil cooler (oil-to-coolant) is standard.
Oil Capacity (including filter): 6.0 liters (6.3 US quarts / 5.3
Imperial quarts).
Recommended Oil Grade: Critical: Must use low-ash, diesel-specific oil
meeting ACEA C3 specification (e.g., 5W-30). This is mandatory for the
longevity of the Diesel Particulate Filter (DPF). API CJ-4 or later is
also acceptable. Operating Oil Pressure: At operating temperature:
294-490 kPa (3.0-5.0 kgf/cm2 / 43-71 psi) at 2,000 rpm.
Type: Pressurized, forced circulation system with separate cooling
circuits for the turbocharger and EGR cooler. Water Pump: Belt-driven
from the crankshaft.
Thermostat: Wax pellet type. Opening temperature is 88°C (190°F).
Radiator Pressure Cap: 108-137 kPa (1.1-1.4 kgf/cm2 / 16-20 psi).
Coolant Capacity: 8.5 liters (9.0 US quarts / 7.5 Imperial quarts).
Coolant Recommendation: Ethylene-glycol based, phosphate-free coolant
meeting Subaru specification (Super Coolant or equivalent).
Auxiliary Electric Water Pump: Used for post-shutdown turbocharger
cooling and cabin heater circulation.
Electrical System: 12-volt DC, negative ground.
Glow Plug System: High-voltage ceramic glow plugs with a dedicated
controller for pre-heat and post-heat cycles. Emission Controls:
Comprehensive system including:
Exhaust Gas Recirculation (EGR): High-pressure and low-pressure loop EGR
with a cooler.
Diesel Oxidation Catalyst (DOC): For reducing CO and HC.
Diesel Particulate Filter (DPF): Traps soot, requires periodic active
regeneration (fuel post-injection) to burn off accumulated particles.
Selective Catalytic Reduction (SCR): On some later/SCR-equipped models,
uses AdBlue (aqueous urea) to reduce NOx emissions.
Sensors: Comprehensive suite including crankshaft/camshaft position,
fuel rail pressure, boost pressure, manifold pressure/temperature, DPF
differential pressure, and NOx sensors (if SCR equipped).
Length (from front of crank pulley to rear of block): 650 mm (25.6
inches).
Width (over cylinder heads): 900 mm (35.4 inches)
Height (from bottom of sump to top of intake manifold): 600 mm (23.6
inches).
Dry Weight (engine only, complete): 185-195 kg (408-430 lbs).
Engine Oil and Filter Change Interval: Critical. Every 10,000 km (6,200
miles) or 12 months, using only ACEA C3 low-ash 5W-30 full synthetic
oil. Extended intervals are not recommended. Fuel Filter: Replace every
20,000 km (12,400 miles) or as specified. Contains a water sensor; water
must be drained regularly. Timing Chain System: Major Known Issue. The
complex chain system is prone to premature stretch, guide wear, and
tensioner failure. Inspection for chain rattle (especially on cold
start) is vital. Complete chain, guide, and tensioner replacement is a
major service, recommended proactively between 120,000-160,000 km
(75,000-100,000 miles).
Valve Clearance Adjustment: Check and adjust every 80,000 km (50,000
miles). Requires significant disassembly. DPF Regeneration: The DPF
requires periodic active regeneration. Frequent short-trip driving
prevents this, leading to clogging. Forced regeneration via diagnostic
tool may be necessary. EGR and Intake System: Prone to severe carbon
buildup. The EGR valve, cooler, and intake manifold should be inspected
and cleaned every 80,000-100,000 km (50,000-62,000 miles). Coolant
Replacement: Every 5 years or 100,000 km (62,000 miles). Air Filter:
Replace every 40,000 km (25,000 miles).
Cylinder Head Bolts (M11): Torque-to-Yield (TTY). Must use new bolts.
Multi-stage angle-torque procedure. Typical Sequence: Step 1: 40 Nm (30
lb-ft). Step 2: +90 deg. Step 3: Loosen completely. Step 4: 40 Nm (30
lb-ft). Step 5: +90 deg again. Always follow exact factory sequence for
each head.
Main Bearing Cap Bolts: 80-85 Nm (59-63 lb-ft).
Connecting Rod Cap Bolts: 45-50 Nm (33-37 lb-ft) + 90-degree turn.
Replace with new bolts.
Crankshaft Pulley Bolt: 340-360 Nm (251-266 lb-ft).
Camshaft Sprocket Bolts: 60-70 Nm (44-52 lb-ft).
Glow Plugs: 15-20 Nm (11-15 lb-ft). Extreme care to avoid breakage.
Fuel Injector Clamp Bolts: 8-10 Nm (5.9-7.4 lb-ft). Precise torque is
critical.
Oil Pan Bolts: 10-15 Nm (7-11 lb-ft).
Rocker Cover Bolts: 8-10 Nm (5.9-7.4 lb-ft).
Intake Manifold Bolts: 20-25 Nm (15-18 lb-ft).
Exhaust Manifold/Integrated Head Nuts: 30-35 Nm (22-26 lb-ft).
The Subaru EE20Z engine was used in a select range of Subaru models
primarily for the European, Australian, and Japanese markets from 2008
to 2016: Subaru Outback (BM/BR, 2008-2014): The primary application,
offered as the "Outback 2.0D" or "Outback Diesel." Subaru Legacy (BM/BR,
2009-2014): The sedan counterpart, sold as the "Legacy 2.0D." Subaru
Forester (SH, 2008-2013): Offered as the "Forester 2.0D" or "Forester
Turbo Diesel."
Subaru Impreza (GH/GE, 2008-2011): Available in the hatchback as the
"Impreza 2.0D" in certain markets. Subaru XV (First Generation,
2012-2016): Offered as the "XV 2.0D" in diesel-preferring markets.
Production ceased due to the high cost of developing the engine to meet
ever-stricter Euro 6 emissions standards, combined with its inherent
complexity and some reliability concerns. It remains a unique,
technologically fascinating, and somewhat notorious chapter in Subaru's
engineering history.
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