Mercedes-Benz OM629 Specifications
| Engine Model: Mercedes-Benz OM629 |
| Engine Type: 4-cycle 8-cylinder DOHC 32-valve twin turbocharger liquid-cooled diesel |
| Total Displacement: 244 cu.in (3.99 L) |
| Rated Engine Power: 302-315 Hp (225-235 kW) at 3600 rpm |
| Fuel System Type: Common rail direct injection |
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The Mercedes-Benz OM629 is a 4.0-liter V8 diesel engine
produced between 2005 and 2013, representing a significant engineering
achievement as the world’s first aluminum-block V8 diesel engine designed for
passenger car applications. Developed as the successor to the OM628, the OM629
was marketed under the 420 CDI and later 450 CDI model designations across
Mercedes-Benz’s executive and luxury vehicle lines.
The engine’s most distinctive architectural feature is its 75° cylinder bank
angle, a departure from the conventional 90° V8 configuration, selected
specifically to reduce the engine’s overall width for installation in the
constrained engine bays of the E-Class, S-Class, and SUV platforms.
The OM629 incorporated several advanced technologies that were state-of-the-art
for its production period. The all-aluminum construction with cast-iron wet
cylinder liners delivered a substantial weight reduction compared to the cast
iron blocks used in competitor diesel V8 engines, contributing to improved
vehicle dynamics and fuel efficiency. The fuel system utilized third-generation
common rail direct injection with piezoelectric injectors operating at pressures
up to 1,600 bar, enabling precise fuel delivery across the operating range.
Twin turbochargers with variable nozzle turbine (VNT) geometry and electric
actuators provided responsive boost delivery while maintaining efficiency. The
engine was equipped exclusively with a diesel particulate filter (DPF) from
introduction, ensuring compliance with Euro 4 emissions standards without
requiring selective catalytic reduction (SCR) systems.
Throughout its production lifecycle, the OM629 appeared in three primary output
configurations. The initial variant produced 225 kW (306 PS / 302 hp) with 700
Nm (516 lb-ft) of torque. A subsequent evolution for the E-Class (W211) raised
output to 231 kW (314 PS / 310 hp) with 730 Nm (538 lb-ft). The final iteration,
introduced with the 450 CDI designation, delivered 235 kW (320 PS / 315 hp)
while maintaining the 730 Nm (538 lb-ft) torque plateau.
Despite its substantial power output, the OM629 achieved remarkable fuel
efficiency for a V8 diesel, with combined cycle consumption figures as low as
9.3 L/100 km (25 mpg US) in the E-Class application. The engine remains highly
regarded among enthusiasts for its combination of refined power delivery, robust
construction, and the distinctive acoustic character of its 75° V8 architecture.
Engine Type: 75° V8, 4-stroke, turbocharged, common rail direct fuel injection
diesel.
Displacement: 3,996 cc (244 cu.in).
Bore: 86.0 mm (3.39 in).
Stroke: 86.0 mm (3.39 in).
Compression Ratio: 17.0:1.
Firing Order: 1-5-4-8-6-3-7-2.
Maximum Power (early 420 CDI): 225 kW (302 hp) @ 3,600 rpm.
Maximum Power (E-Class 420 CDI): 231 kW (310 hp) @ 3,600 rpm.
Maximum Power (450 CDI): 235 kW (315 hp) @ 3,600 rpm.
Maximum Torque (420 CDI): 700 Nm (516 lb-ft) @ 2,000-2,600 rpm.
Maximum Torque (450 CDI): 730 Nm (538 lb-ft) @ 2,000-2,600 rpm.
Idle Speed: 580-620 rpm, electronically governed.
Redline: 4,600 rpm with fuel cut-off at 4,800 rpm.
Aspiration: Twin turbochargers with variable nozzle turbine (VNT) geometry, each
equipped with independent electric actuators.
Charge Air Cooling: Air-to-water intercooler system integrated into the intake
manifold assembly.
The cylinder block is constructed from a high-strength
aluminum-silicon alloy, marking the first application of an aluminum V8 diesel
block in a production passenger car. This material selection reduced the
engine’s mass by approximately 60 kg (132 lb) relative to a comparable cast iron
V8 diesel. The block utilizes a closed-deck design to provide rigidity under the
high cylinder pressures associated with diesel combustion.
Cylinder liners are cast-iron wet-sleeve type, pressed into the aluminum block
and sealed at the top and bottom with elastomeric O-rings. This liner
configuration allows for replacement during major overhauls while providing the
necessary wear resistance for the piston rings. The wet liner design also
contributes to uniform cooling around each cylinder bore.
The crankcase incorporates a deep-skirt design with cross-bolted main bearing
caps. The main bearing caps are manufactured from sintered steel and are secured
with four bolts each - two vertical bolts through the cap and two horizontal
cross-bolts through the side of the block. This cross-bolted arrangement
provides exceptional crankshaft support under the high peak cylinder pressures
characteristic of turbocharged diesel engines.
Main Bearing Journal Diameter: 65.0 mm (2.56 in).
Connecting Rod Journal Diameter: 55.0 mm (2.17 in).
Piston Material: Forged aluminum alloy with anodized ring grooves and a
graphite-coated skirt. Piston Cooling: Oil spray jets mounted in the cylinder
block direct a continuous stream of engine oil to the underside of each piston
crown, managing thermal loads exceeding 300 °C (572 °F) under full load.
Crankshaft: Forged steel with eight counterweights, induction-hardened bearing
surfaces.
Connecting Rods: Forged steel, fracture-split construction with a trapezoidal
small end design to reduce reciprocating mass. Balancer Shaft: A balancer shaft
is mounted within the 75° V-angle of the cylinder banks, rotating at engine
speed to counteract first-order inertial forces inherent to the 75° V8
configuration.
Four individual cylinder heads are utilized - two per
cylinder bank - each covering two cylinders. This modular head configuration
reduces thermal stress and allows for more efficient casting and machining
processes. Each head is manufactured from aluminum alloy and houses the
valvetrain for its respective two cylinders.
Valvetrain: DOHC configuration with four valves per cylinder (32 total). Each
cylinder bank features two chain-driven camshafts. The camshafts are driven from
the rear of the engine through a primary chain system connected to the
crankshaft, with secondary chains transferring drive to the individual heads.
Intake Valve Diameter: 32.0 mm (1.26 in).
Exhaust Valve Diameter: 28.5 mm (1.12 in).
Valve Lift (Intake): 9.5 mm (0.374 in).
Valve Lift (Exhaust): 9.5 mm (0.374 in).
Valve Adjustment: Hydraulic valve lash adjusters are integrated into the cam
followers, eliminating the need for periodic valve clearance adjustment. Valve
Seat Material: High-strength sintered alloy with induction-hardened contact
surfaces. Valve Spring Material: High-tensile steel with a beehive design to
reduce reciprocating mass and prevent valve float at elevated engine speeds.
Camshaft Drive: Chain-driven system with a primary chain from the crankshaft to
an intermediate shaft, and secondary chains from the intermediate shaft to each
of the four camshafts. An automatic hydraulic tensioner maintains proper chain
tension throughout the engine’s service life.
The fuel system is a third-generation common rail
direct injection system manufactured by Bosch. The system operates at pressures
up to 1,600 bar (23,200 psi) and utilizes piezoelectric injectors for precise
fuel delivery.
Fuel Injectors: Piezoelectric direct-acting injectors with eight nozzle orifices
per injector. Piezoelectric technology allows for multiple injection events per
combustion cycle - up to five separate injections - including pilot, main,
post-injection, and after-injection events. This capability reduces combustion
noise, optimizes emissions, and enables particulate filter regeneration.
High-Pressure Fuel Pump: Bosch CP3 two-piston radial-piston pump driven by the
engine’s front timing gears. The pump delivers fuel to a common rail shared
across all eight cylinders. Common Rail Pressure: 300-1,600 bar (4,350-23,200
psi), regulated by a pressure control valve on the pump and a pressure relief
valve on the rail.
Low-Pressure Fuel System: 4.0-6.0 bar (58-87 psi) supplied by an electric lift
pump located within the fuel tank. Fuel Filter: Spin-on type with integrated
water separator and water-in-fuel sensor. Fuel Requirement: Diesel fuel meeting
EN 590 specification with sulfur content below 10 ppm.
The lubrication system is a fully pressurized wet-sump
design with a gear-type oil pump mounted on the front of the engine. The pump is
driven directly by the crankshaft and incorporates a pressure relief valve to
maintain consistent oil pressure across the operating range. Oil Pump Type:
Dual-stage gear pump with integrated oil cooler bypass thermostat.
Recommended Oil Viscosity: 5W-30 or 5W-40 fully synthetic, meeting Mercedes-Benz
specification MB 229.3, MB 229.5, or MB 229.51 (low-ash formulation for
DPF-equipped engines). Oil Capacity (with filter change): 9.5 liters (10.0 qt).
Oil Pressure (at idle, warm): 1.5-2.5 bar (22-36 psi). Oil Pressure (at 3,000
rpm, warm): 4.5-5.5 bar (65-80 psi).
Oil Filter Type: Spin-on full-flow filter with integral bypass valve and
anti-drainback valve. Oil Cooler: Plate-type coolant-to-oil heat exchanger
mounted on the lower right side of the engine. Oil Pan: Stamped steel with
integrated baffling and a capacity of 8.5 liters (9.0 qt) exclusive of filter
and cooler oil volume.
The cooling system is a pressurized, thermostatically
controlled circuit utilizing a belt-driven centrifugal water pump. The system
incorporates split water jackets in the cylinder heads, a design that directs
coolant flow first to the exhaust valve bridge areas - the region of highest
thermal stress - before routing coolant to the remainder of the head.
Water Pump Type: Centrifugal with a mechanical seal, driven by the serpentine
accessory belt. Coolant Type: Ethylene-glycol based antifreeze meeting
Mercedes-Benz specification MB 325.0. Coolant Capacity (engine and radiator):
12.5 liters (13.2 qt). Thermostat: Dual-stage wax-type thermostat with an
opening temperature of 83 °C (181 °F) for the primary circuit and 88 °C (190 °F)
for the secondary circuit.
Radiator: High-efficiency cross-flow aluminum radiator with integrated coolant
expansion tank. Cooling Fan: Electric viscous clutch fan with on-demand
engagement, supplemented by an electric auxiliary fan for air conditioning
condenser and low-speed cooling requirements.
Charge Air Cooling: Separate air-to-water intercooler system with a dedicated
low-temperature coolant circuit. An electric coolant pump circulates coolant
through the intercooler heat exchangers mounted within the intake manifolds,
with heat rejection handled by a separate radiator mounted in front of the main
engine radiator.
Exhaust System: Dual exhaust manifolds, one per
cylinder bank, constructed from stainless steel. The exhaust system incorporates
two close-coupled diesel oxidation catalysts (DOC) and a single diesel
particulate filter (DPF) located downstream of the turbochargers. The DPF
utilizes passive and active regeneration strategies, with post-injection fuel
delivery to raise exhaust temperatures during active regeneration.
Exhaust Gas Recirculation: High-pressure EGR system with coolers integrated into
each cylinder bank. EGR rates of up to 25% are utilized to reduce nitrogen oxide
(NOx) emissions.
Timing Drive: Dual-chain system with primary and
secondary chains. The primary chain drives from the crankshaft to an
intermediate shaft located at the rear of the engine. Secondary chains drive
each of the four camshafts from the intermediate shaft. All chains utilize
hydraulic tensioners with mechanical ratcheting mechanisms.
Accessory Drive: Single 8-rib serpentine belt driving the alternator, water
pump, power steering pump, and air conditioning compressor. An automatic
spring-loaded tensioner maintains consistent belt tension.
Turbochargers: Two variable nozzle turbine (VNT) turbochargers, one per cylinder
bank. Each turbocharger is equipped with an electric actuator that adjusts the
vane geometry to optimize boost pressure across the engine speed range. Maximum
boost pressure is 2.2 bar absolute (32 psi gauge) under full load conditions.
Engine Management System: Bosch EDC16 CP31 or later EDC17 electronic diesel
control system. The ECU manages fuel injection timing, injection pressure, boost
pressure, variable nozzle turbine actuation, exhaust gas recirculation (EGR),
and DPF regeneration.
Emissions Compliance: Euro 4 with Diesel Particulate Filter (DPF) from
introduction. Later variants achieved Euro 5 compliance through calibration
updates and improved aftertreatment management.
Overall Length: 750 mm (29.5 in)
Overall Width: 750 mm (29.5 in)
Overall Height: 720 mm (28.3 in)
Dry Weight (complete engine): 220 kg (485 lb)
Engine Oil and Filter Change: 12 months or 15,000 km
(9,000 mi) under flexible service intervals; 20,000 km (12,000 mi) under fixed
interval programming. Severe service conditions, including frequent trailer
towing, extensive city driving, or operation in dusty environments, require
reduced intervals.
Timing Chain: No scheduled replacement interval. Inspection of chain tension and
camshaft correlation is recommended at 150,000 km (93,000 mi) and every 50,000
km (31,000 mi) thereafter. Chain stretch may occur with extended oil change
intervals.
Fuel Filter: Replace every 30,000 km (18,000 mi) or 2 years. Engine Air Filter
Element: Replace every 30,000 km (18,000 mi); more frequent replacement required
in dusty environments. Coolant Replacement: 150,000 km (93,000 mi) or 10 years,
then every 60,000 km (37,000 mi) or 5 years thereafter.
Drive Belt Inspection: Every 15,000 km (9,000 mi) for cracks, fraying, glazing,
and proper tension. Drive Belt Replacement: 90,000 km (56,000 mi) or 6 years.
Valve Clearance: Hydraulic lash adjusters eliminate the need for valve clearance
inspection or adjustment throughout the engine’s service life.
Diesel Particulate Filter: DPF regeneration occurs automatically under normal
driving conditions. Ash accumulation requires filter replacement at
approximately 150,000-200,000 km (93,000-124,000 mi) depending on operating
conditions and oil consumption.
Cylinder Head Bolts, Step 1: 40 Nm (30 lb-ft)
Cylinder Head Bolts, Step 2: 60 Nm (44 lb-ft) + 90° turn
Main Bearing Cap Bolts (vertical), Step 1: 30 Nm (22 lb-ft)
Main Bearing Cap Bolts (vertical, Step 2: 70 Nm (52 lb-ft) + 90° turn
Main Bearing Cross Bolts (horizontal), Step 1: 30 Nm (22 lb-ft)
Main Bearing Cross Bolts (horizontal), Step 2: 60 Nm (44 lb-ft)
Connecting Rod Cap Bolts: 30 Nm (22 lb-ft) + 90° turn
Camshaft Bearing Caps: 12 Nm (9 lb-ft)
Camshaft Drive Chain Tensioners: 40 Nm (30 lb-ft)
Intake Manifold to Cylinder Head: 15 Nm (11 lb-ft)
Exhaust Manifold to Cylinder Head: 25 Nm (18 lb-ft) + 90° turn
Turbocharger to Exhaust Manifold: 25 Nm (18 lb-ft)
Turbocharger Oil Feed Lines: 25 Nm (18 lb-ft)
High-Pressure Fuel Pump Mounting Bolts: 20 Nm (15 lb-ft)
Common Rail Mounting Bolts: 25 Nm (18 lb-ft)
Fuel Injector Clamp Bolts: 8 Nm (6 lb-ft) + 270° turn
Oil Pan Bolts: 15 Nm (11 lb-ft) + 90° turn
Valve Cover Bolts: 10 Nm (7 lb-ft)
Flywheel / Flexplate Bolts: 60 Nm (44 lb-ft) + 90° turn
Crankshaft Pulley Bolt: 200 Nm (148 lb-ft) + 90° turn
Engine Mount Brackets to Block: 40 Nm (30 lb-ft)
The OM629 engine was installed across Mercedes-Benz’s
passenger car and light truck product lines from 2005 through 2013, appearing in
both 420 CDI and 450 CDI model designations.
Mercedes-Benz E-Class (W211, 2005-2009): The E 420 CDI represented the first
application of the OM629, delivering 231 kW (314 hp) and 730 Nm (538 lb-ft).
This model achieved a combined fuel consumption of 9.3 L/100 km (25 mpg US) and
was offered exclusively with the 7G-Tronic seven-speed automatic transmission.
Mercedes-Benz S-Class (W221, 2006-2010): The S 420 CDI utilized the OM629 in 225
kW (302 hp) configuration from 2006 through 2009, with the S 450 CDI replacing
it from 2009 to 2010, delivering 235 kW (320 hp). These models featured the same
7G-Tronic transmission and were available in both standard and long-wheelbase
configurations.
Mercedes-Benz CL-Class (C216, 2007-2010): The CL 420 CDI received the OM629 in
225 kW (302 hp) form, offering the V8 diesel powertrain in the luxury coupe body
style.
Mercedes-Benz ML-Class (W164, 2007-2010): The ML 420 CDI and later ML 450 CDI
utilized the OM629 with outputs of 225 kW (302 hp) and 235 kW (320 hp)
respectively. In the ML application, the engine was paired with the 7G-Tronic
transmission and featured a full-time 4MATIC all-wheel-drive system.
Mercedes-Benz GL-Class (X164, 2006-2010): The GL 420 CDI and GL 450 CDI
represented the OM629 in the full-size luxury SUV platform. The GL application
required specific cooling system modifications to accommodate the engine in the
larger SUV engine bay while maintaining adequate airflow for the intercooler and
main radiator systems.
Mercedes-Benz R-Class (W251, 2007-2010): The R 420 CDI and R 450 CDI received
the OM629 in select markets, providing the V8 diesel powertrain in the large
multi-purpose vehicle (MPV) body style.
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