Subaru EJ253 Specifications
| Engine Model: Subaru EJ253 |
| Engine Type: 4-cycle 4-cylinder SOHC 16-valve liquid-cooled gasoline |
| Total Displacement: 149.9 cu.in (2.45 L) |
| Rated Engine Power: 165-175 Hp (123-130 kW) at 5600 rpm |
| Fuel System Type: Multi-point electronic fuel injection |
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The Subaru EJ253 is a 2.5-liter naturally aspirated
flat-four engine that served as the primary powertrain for Subaru’s non-turbo
vehicle lineup for over a decade. Introduced in 1999, the EJ253 represents the
most common variant of the SOHC EJ25 series, engineered to prioritize low-end
torque, fuel efficiency, and emissions compliance over high-rpm power. The
engine features an all-aluminum construction with a horizontally opposed
cylinder layout, a single overhead camshaft per cylinder bank operating four
valves per cylinder, and multi-point fuel injection.
From 2006 onward, the EJ253 incorporated i-AVLS (i-Active Valve Lift System),
which varied intake valve lift to optimize performance across the operating
range. The engine was offered in Partial Zero Emission Vehicle (PZEV)
configurations in certain markets, incorporating dual catalytic converters and
revised calibration to meet stringent emissions standards.
Engine Type: Horizontally opposed 4-cylinder (flat-4), 4-cycle, naturally
aspirated gasoline.
Displacement: 2,457 cc (149.9 cu.in).
Bore: 99.5 mm (3.92 in).
Stroke: 79.0 mm (3.11 in).
Compression Ratio: 10.0:1 for early variants (1999-2005).
Compression Ratio: 10.2:1 for later variants (2006-2012) with i-AVLS.
Firing Order: 1-3-2-4.
Maximum Power 165-175 hp (123-130 kW) @ 5,600 rpm.
Maximum Torque 225-230 Nm (166-170 lb-ft) @ 4,000-4,400 rpm.
Valvetrain Configuration: Single Overhead Camshaft (SOHC) per cylinder bank,
operating 16 valves (4 valves per cylinder). The camshafts are driven by a
toothed timing belt. Hydraulic lash adjusters are incorporated, eliminating
routine manual valve clearance adjustments. Post-2006 variants utilize i-AVLS
(i-Active Valve Lift System) on the intake valves.
The cylinder block is manufactured from aluminum alloy
with a horizontally opposed configuration. Bore diameter measures 99.5 mm (3.92
in). The block features an open-deck design, where the cylinder bores are open
to the water jacket at the top, providing efficient cooling at the expense of
reduced cylinder wall support compared to closed-deck designs.
The crankshaft is forged steel with eight
counterweights, supported by five main bearings. The Phase II block
design incorporates the thrust bearing at the number five main bearing
position (rear). The cylinder bores are machined with a plateau honed
finish and utilize cast iron liners integrally cast into the block.
Each cylinder head is manufactured from aluminum alloy
with a cross-flow port architecture.
Valves: 16 total; 8 intake, 8 exhaust.
Intake Valve Diameter: 35.0 mm (1.38 in).
Exhaust Valve Diameter: 30.0 mm (1.18 in).
Valve Stem Diameter: 6.0 mm (0.24 in) for both intake and exhaust.
Valve Seat Inserts: Powder metal sintered alloy with multi-angle seat geometry.
Valve Guides: Press-fit sintered iron guides.
Hydraulic Lash Adjusters: Direct-acting units mounted in the cylinder head
casting, operating on rocker arms or bucket-type followers depending on
production year. Camshafts: Chilled cast iron camshafts with induction-hardened
lobes. Each bank utilizes a single camshaft operating both intake and exhaust
valves through rocker arms. Valve Springs: Progressive-rate springs designed for
the i-AVLS switching mechanism.
i-AVLS System: Introduced in 2006, the i-Active Valve Lift System varies the
lift of one intake valve per cylinder. The system uses two distinct cam profiles
per valve: a low-lift profile (5.5 mm lift) for low-speed operation and a
high-lift profile (approximately 9.0 mm lift) for high-speed operation. A
hydraulic switching mechanism, controlled by the engine control unit via oil
pressure, engages the high-lift profile above approximately 3,500 rpm.
The fuel system employs multi-point fuel injection with
sequential injection timing. Injection Type: Sequential multi-port injection
with fuel injectors positioned in the intake manifold runners adjacent to each
intake port.
Engine Management System: Subaru ECU utilizing either a MAP (Manifold Absolute
Pressure) sensor or MAF (Mass Air Flow) sensor depending on model year and
emissions specification. PZEV variants utilize a MAF sensor with dual catalytic
converters and revised calibration.
Fuel Pressure: Regulated to 3.0-3.5 bar (44-51 psi) via a vacuum-referenced fuel
pressure regulator. Injector Flow Rate: 270-300 cc/min at standard operating
pressure. Fuel Pump: In-tank electric fuel pump with flow rate calibrated for
the engine’s output.
Intake Manifold: Composite plastic or aluminum manifold with individual runners
per cylinder. The manifold incorporates a resonance chamber and is equipped with
an electronically controlled throttle body.
The lubrication system is a full-flow, pressurized
design utilizing a rotor-type oil pump driven by the crankshaft. Oil Pump Type:
Internal gear (gerotor) pump mounted to the front of the crankshaft, housed
within the front timing cover assembly. Oil Capacity: 4.5-5.0 liters (4.8-5.3
qt) including oil filter replacement. Recommended Oil Viscosity: 5W-30 or
10W-30. Oil Quality Requirement: API SL, SM, SN, or later classifications.
Oil Pressure: At warm idle, pressure ranges from 1.0-1.5 bar (14-22 psi). At
3,000 rpm, pressure reaches 3.5-4.5 bar (51-65 psi). Oil Cooler: Liquid-to-oil
plate-type heat exchanger is integrated into the oil filter housing on certain
variants, particularly those equipped for towing or PZEV configurations. Oil
Filter: Full-flow spin-on canister type mounted to the engine block. Crankcase
Ventilation: Closed PCV system with a PCV valve mounted in the intake manifold.
The cooling system is pressurized and utilizes a
centrifugal water pump driven by the timing belt. Water Pump Type: Centrifugal
pump with a cast aluminum housing and stamped steel impeller. Thermostat:
Wax-pellet type located in the coolant outlet housing. Opening temperature is
76-82 °C (169-180 °F). Coolant Capacity: 6.0-7.0 liters (6.3-7.4 qt) inclusive
of engine block, heater core, and radiator.
Radiator: Cross-flow aluminum core with plastic end tanks. Cooling fan
configuration consists of dual electric fans with variable speed control based
on coolant temperature and air conditioning load. System Pressure: Radiator cap
rated at 1.1 bar (16 psi). Coolant Specification: Phosphate and silicate-free
ethylene glycol-based coolant meeting Subaru specifications for aluminum engine
construction.
Ignition System: Distributorless ignition system with
individual ignition coils (coil-on-plug) for each cylinder. The system utilizes
a crankshaft position sensor and dual camshaft position sensors for sequential
ignition timing. Spark Plug Type: NGK BKR5E-11 or equivalent. Spark Plug Gap:
1.0-1.1 mm (0.039-0.043 in).
Timing System: Toothed timing belt constructed from high-tensile rubber with
fiber reinforcement. The belt drives the camshafts on both cylinder banks and
the water pump. An automatic spring-loaded tensioner maintains belt tension. The
engine is interference; timing belt failure results in piston-to-valve contact.
Replacement interval is 168,000 km (105,000 miles) or 105 months.
Exhaust System: Cast iron exhaust manifolds per cylinder bank merging into a
single exhaust pipe. PZEV variants utilize dual catalytic converters
(pre-catalyst and main catalyst) with close-coupled positioning for rapid
light-off.
Intake System: Air induction utilizes a large-volume air cleaner housing with a
replaceable paper element. The air cleaner incorporates a cold-air intake duct
positioned to draw ambient air from outside the engine compartment.
Overall Length: 720 mm (28.3 in) measured from
accessory drive pulley face to transmission mounting flange.
Overall Width: 750 mm (29.5 in) inclusive of intake manifold, throttle body, and
exhaust manifolds.
Overall Height: 600 mm (23.6 in) from oil pan bottom surface to valve cover top
surface.
Dry Weight: 115-125 kg (254-276 lb) depending on intake manifold configuration
and accessory drive components.
Valve Clearance: Hydraulic lash adjusters operate
automatically. No periodic adjustment required. Timing Belt Replacement
Interval: 168,000 km (105,000 miles) or 105 months. Replacement includes belt,
tensioner, idler pulleys, and water pump. Spark Plug Replacement Interval:
48,000 km (30,000 miles) for standard plugs.
Drive Belt Tension (Accessory): 8-10 mm (0.31-0.39 in) deflection under 10 kg
(22 lb) of force at the midpoint of the longest span. Automatic tensioners are
used on later variants. Coolant Change Interval: 48,000 km (30,000 miles) or 2
years. Engine Oil Change Interval: 7,500-10,000 km (4,700-6,200 miles) depending
on operating conditions and oil quality.
Idle Speed (warm, neutral): 700-750 rpm. Ignition Timing: Electronically
controlled with no manual adjustment provision. Fuel Pressure: 3.0-3.5 bar
(44-51 psi) with vacuum line disconnected from fuel pressure regulator.
Compression Pressure: Standard 1.3-1.5 MPa (189-218 psi) per cylinder; minimum
1.0 MPa (145 psi). Maximum variation between cylinders is 0.1 MPa (14 psi).
Cylinder Head Bolts (cold), Step 1: 30 Nm (22 lb-ft).
Cylinder Head Bolts (cold), Step 2: 50 Nm (37 lb-ft).
Crankshaft Damper Pulley Bolt: 180-200 Nm (133-148 lb-ft).
Connecting Rod Cap Bolts: 40-45 Nm (30-33 lb-ft).
Main Bearing Cap Bolts: 60-65 Nm (44-48 lb-ft).
Camshaft Bearing Cap Bolts: 20-25 Nm (15-18 lb-ft).
Camshaft Sprocket Bolts: 60-70 Nm (44-52 lb-ft).
Valve Cover Bolts: 8-10 Nm (6-7 lb-ft).
Intake Manifold Bolts: 20-25 Nm (15-18 lb-ft).
Exhaust Manifold Nuts: 30-35 Nm (22-26 lb-ft).
Oil Pan Bolts: 10-12 Nm (7-9 lb-ft).
Oil Pump Mounting Bolts: 10-12 Nm (7-9 lb-ft).
Timing Belt Tensioner Bolt: 25-30 Nm (18-22 lb-ft).
Water Pump Bolts: 20-25 Nm (15-18 lb-ft).
Flywheel / Drive Plate Bolts: 80-90 Nm (59-66 lb-ft).
Engine Mount Bracket Bolts: 45-55 Nm (33-41 lb-ft).
Spark Plugs: 20-25 Nm (15-18 lb-ft).
Subaru Impreza (2.5i / RS): 2004-2011 model years. The
EJ253 powered the naturally aspirated Impreza 2.5i and RS variants in North
American and global markets, serving as the base engine for sedan, hatchback,
and wagon body styles.
Subaru Legacy / Liberty (2.5i): 1999-2012 model years. The EJ253 was the primary
powertrain for the Legacy and Liberty 2.5i across three generations (BE/BH,
BL/BP, and early BM/BR), with i-AVLS introduced in 2006.
Subaru Outback (2.5i): 2000-2012 model years. The EJ253 powered the Outback 2.5i
wagon across multiple generations, receiving the i-AVLS system in 2006.
Subaru Forester (X / XS): 1999-2010 model years. The EJ253 was installed in the
Forester X and XS trims, providing the entry-level and mid-range powertrain
options for the compact SUV.
Subaru Baja: 2003-2006 model years. The EJ253 served as the standard engine for
the Baja light truck, a vehicle combining pickup utility with Subaru’s
all-wheel-drive system.
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