Mercedes-Benz OM639 Specifications
| Engine Model: Mercedes-Benz OM639 |
| Engine Type: 4-cycle 3-cylinder DOHC 12-valve turbocharged liquid-cooled diesel |
| Total Displacement: 91.1 cu.in (1.49 L) |
| Rated Engine Power: 67-94 Hp (50-70 kW) at 4000 rpm |
| Fuel System Type: Common rail direct injection |
____________________________________________________________________________________
The Mercedes-Benz OM639 is a turbocharged inline-three
diesel engine produced between 2004 and 2009. Developed in collaboration with
Mitsubishi Motors, it was based on the four-cylinder OM640 engine and stood out
as the world’s most powerful three-cylinder passenger car diesel engine at the
time of its release. The OM639 features a compact, lightweight design with a
cast-iron block and an aluminum alloy cylinder head.
It is transversely mounted and inclined at 60 degrees to accommodate the
sandwich floor safety design of its target vehicles, a configuration that
allowed for optimized crash energy absorption while maintaining a low hood line.
This engine represented a significant engineering achievement in downsizing,
delivering performance characteristics comparable to larger displacement
four-cylinder diesels while offering superior packaging efficiency.
The collaboration with Mitsubishi brought advanced manufacturing techniques and
shared componentry, yet the engine retained Mercedes-Benz’s rigorous standards
for durability and refinement. The OM639’s production run was relatively short,
coinciding with the lifecycle of the Smart Forfour and the Mitsubishi Colt, but
it remains a notable example of early 2000s diesel technology where power
density, fuel efficiency, and emissions compliance were balanced within a
diminutive footprint.
The OM639 is a four-stroke, water-cooled diesel engine operating on the
compression-ignition principle. The engine architecture is an inline-three
cylinder configuration with a 60-degree transverse inclination when installed, a
layout chosen specifically for the platform-sharing arrangement between Smart
and Mitsubishi. The total displacement measures 1,493 cc (91.1 cu.in), derived
from a bore of 83.0 mm (3.27 in) and a stroke of 92.0 mm (3.62 in).
This long-stroke design promotes low-end torque generation, a critical
characteristic for diesel engines intended for urban driving and light
commercial applications. The compression ratio is fixed at 18.0:1 across all
variants, a value that balances cold-start capability with combustion
efficiency.
The engine utilizes a dual overhead camshaft (DOHC) valvetrain with four valves
per cylinder, totaling twelve valves. The firing order for this three-cylinder
engine is 1-2-3, with uneven firing intervals of 240 degrees of crankshaft
rotation, a characteristic that necessitates the use of a balancer shaft to
mitigate inherent first-order vibrations. The rated speed is governed at 4,000
rpm to 4,400 rpm depending on the variant, with the maximum power and torque
peaks occurring at lower engine speeds to preserve longevity and drivability.
Two distinct performance variants exist within the OM639 family. The reduced
power variant, designated OM639 DE15 LA R, delivers 50 kW (67 hp) at 4,000 rpm
and 160 Nm (118 lb-ft) of torque at 1,600 rpm to 2,600 rpm. The standard output
variant, designated OM639 DE15 LA, produces 70 kW (94 hp) at 4,000 rpm and 210
Nm (155 lb-ft) of torque across a plateau from 1,800 rpm to 2,500 rpm.
The cylinder block is manufactured from gray cast iron,
providing the necessary structural rigidity to withstand combustion pressures
inherent to turbocharged diesel operation. The block features an open-deck
design, which reduces weight and improves cooling efficiency around the cylinder
bores. Unlike larger heavy-duty engines, the OM639 utilizes a monoblock
construction with integral cylinder bores rather than replaceable liners. The
cylinder bores are finished with a plateau honing process that optimizes oil
retention and ring sealing during the break-in period.
The crankcase incorporates a deep-skirt configuration extending below the
crankshaft centerline, enhancing overall stiffness and reducing noise
transmission. The engine mounting points are designed specifically for
transverse installation, with provisions for the 60-degree inclination used in
the Smart Forfour and Mitsubishi Colt platforms. A balancer shaft is housed
within the crankcase, driven by the oil pump chain. This shaft rotates at twice
the engine speed to counteract the first-order rocking couple inherent to
three-cylinder engines, ensuring refinement comparable to four-cylinder units.
The cylinder head is manufactured from aluminum alloy,
a choice that reduces overall engine weight and improves thermal conductivity
for more efficient heat dissipation. It features a dual overhead camshaft (DOHC)
arrangement, with each camshaft driven by a maintenance-free timing chain. The
chain drive system incorporates hydraulic tensioners and guide rails to maintain
precise timing over the engine’s service life.
Each cylinder houses four valves - two intake and two exhaust - arranged in a
pent-roof combustion chamber design that optimizes swirl and tumble
characteristics for efficient mixture formation. The valves are actuated by
finger followers with hydraulic lash adjusters, eliminating the need for
periodic valve clearance adjustments. The intake valves are larger in diameter
than the exhaust valves to maximize volumetric efficiency under turbocharged
conditions.
The valve seat inserts are manufactured from sintered metal alloys selected for
heat resistance and wear durability. The exhaust valves are sodium-filled in
certain applications to improve heat transfer from the valve head to the valve
guide. The cylinder head gasket is a multi-layer steel (MLS) design, providing
robust sealing under the high cylinder pressures generated by the common rail
fuel system.
The OM639 is equipped with a second-generation common
rail direct injection system developed in collaboration with Bosch. This system
operates at injection pressures up to 1,600 bar (23,206 psi), a significant
advancement over earlier diesel systems and a key enabler for the engine’s
combination of power output and emissions compliance. A high-pressure pump,
mounted at the rear of the engine and driven by the timing chain, draws fuel
from the tank and supplies the common rail accumulator.
The rail distributes pressurized fuel to solenoid injectors located centrally
within each cylinder head. These injectors are capable of multiple injection
events per combustion cycle, including pre-injection, main injection, and
post-injection. Pre-injection reduces combustion noise and improves cold-start
behavior, while post-injection raises exhaust gas temperatures to facilitate
regeneration of the diesel particulate filter where fitted. The fuel system is
managed by an electronic control unit that monitors crankshaft position,
accelerator pedal position, boost pressure, and fuel rail pressure to calculate
injection timing and duration with high precision.
A notable feature of the engine management system is the synchronization without
a dedicated camshaft sensor; instead, the system uses a high-resolution
crankshaft position sensor to virtually generate camshaft position information,
reducing component count and increasing reliability. The fuel filtration system
includes a water separator and a fine filter to protect the high-pressure
components from contamination.
The lubrication system is a forced-feed, full-flow
filtration design utilizing a gear-type oil pump. The oil pump is driven by a
chain from the crankshaft and is mounted within the oil pan for direct pickup.
The system maintains stable oil pressure across the operating range, with a
pressure relief valve calibrated to open at 4.5 bar (65 psi). An oil cooler, of
the plate-and-fin type, is integrated into the engine coolant circuit to
maintain oil viscosity under sustained high-load conditions.
The engine employs a full-flow spin-on oil filter with an integrated bypass
valve that opens if the filter becomes restricted, ensuring continued oil supply
to critical components. The oil pan is constructed from stamped steel and is
designed to accommodate the transverse engine inclination, with the oil pickup
positioned to maintain suction under cornering and braking maneuvers. The total
oil capacity, including the filter, is 4.5 liters (4.8 US qt). The balancer
shaft assembly is integrated into the lubrication circuit, with dedicated oil
galleries supplying the shaft bearings.
The cooling system is a pressurized, water-cooled
design utilizing a centrifugal water pump driven by the accessory drive belt.
The system maintains engine operating temperature within a range of 85°C to 95°C
(185°F to 203°F) under normal conditions. The coolant circuit incorporates a
thermostatic bypass that facilitates rapid warm-up during cold starts, reducing
internal friction and improving fuel economy. The cylinder head features
optimized coolant passages that direct flow preferentially to the exhaust valve
bridge areas, the hottest regions within the combustion chamber.
The charge air cooler (intercooler) is an air-to-air unit mounted in the
vehicle’s front-end cooling package, reducing the temperature of compressed air
from the turbocharger from approximately 150°C (302°F) to 50°C (122°F) before it
enters the intake manifold. This cooling of the intake charge increases air
density and combustion efficiency, directly contributing to the engine’s power
output. An electric cooling fan supplements the radiator at low vehicle speeds
and during idle conditions. The total coolant capacity for the engine and
cooling system is approximately 6.5 liters (6.9 US qt).
Air Intake and Turbocharging: The engine is equipped
with a fixed-geometry turbocharger manufactured by Mitsubishi or Garrett,
depending on production date. The turbocharger is mounted directly to the
exhaust manifold, a compact arrangement that minimizes turbo lag. The intake
system includes a mass air flow sensor, an intake air temperature sensor, and a
throttle valve used primarily for exhaust gas recirculation control rather than
for engine power regulation.
Engine Management: The OM639 utilizes a Bosch EDC16 electronic control unit.
This system monitors crankshaft position, camshaft position (virtually derived),
boost pressure, intake air temperature, coolant temperature, fuel rail pressure,
and exhaust gas oxygen content. It controls injection timing, injection
quantity, boost pressure via a wastegate actuator, and the exhaust gas
recirculation valve position.
Exhaust System: To comply with Euro 4 emission standards, the exhaust system
incorporates a cooled exhaust gas recirculation (EGR) system. The EGR cooler
reduces the temperature of recirculated exhaust gas, lowering combustion
temperatures and reducing NOx formation. Depending on market specifications, a
diesel oxidation catalyst and a diesel particulate filter are also present in
the exhaust tract. The exhaust manifold is constructed from cast iron to
withstand thermal cycling.
The engine length, measured from the accessory drive
pulley to the flywheel housing face, is 550 mm (21.7 in). The width is 620 mm
(24.4 in) at the widest point, which includes the turbocharger and exhaust
manifold. The height, measured from the oil pan bottom to the top of the
cylinder head cover, is 650 mm (25.6 in).
The dry weight (without fluids, starter,
alternator, or air conditioning compressor) is 125 kg (276 lb). The
fully dressed weight for a vehicle application, including all
accessories, wiring harness, and fluids, is 145 kg (320 lb).
The service life of the OM639 under proper operating
conditions is engineered to exceed 250,000 km (155,000 mi) with regular
maintenance. Oil change intervals are determined by the engine management system
based on operating conditions, with a maximum interval of 30,000 km (18,600 mi)
or 24 months under favorable conditions. For severe service conditions,
including frequent short trips or high-load operation, the recommended interval
is reduced to 15,000 km (9,300 mi). The engine requires a low-ash, synthetic
5W-30 or 5W-40 engine oil meeting Mercedes-Benz specification 229.31 or 229.51.
The timing chain is designed for the service life of the engine and does not
require replacement under normal operating conditions, though tensioner and
guide rail inspection is recommended at 150,000 km (93,000 mi). Replacement of
the fuel filter is mandated every 60,000 km (37,000 mi) or 48 months.
The air cleaner element requires replacement every 60,000 km (37,000 mi), with
more frequent servicing in dusty environments. The coolant must be replaced
every 5 years or 200,000 km (124,000 mi), using a nitrite-free, long-life
coolant formulation. The accessory drive belt requires inspection at each
service interval, with replacement recommended every 90,000 km (56,000 mi) or
sooner if cracking or wear is evident.
The cylinder head bolts follow a multi-stage angular
torque procedure. The M10 cylinder head bolts receive an initial torque of 40 Nm
(30 lb-ft), followed by a 90-degree angle, and a final 90-degree angle in a
specified sequence. The main bearing cap bolts are torqued to 50 Nm (37 lb-ft)
plus a 90-degree angle. The connecting rod bolts are tightened to 30 Nm (22
lb-ft) plus a 90-degree angle.
The flywheel-to-crankshaft bolts receive a torque of 60 Nm (44 lb-ft) plus a
90-degree angle. The camshaft bearing caps are torqued to 12 Nm (9 lb-ft) plus a
30-degree angle. The injector hold-down bolts require 9 Nm (7 lb-ft) plus a
90-degree angle. The timing chain tensioner bolt is torqued to 25 Nm (18 lb-ft).
The balancer shaft bearing caps are torqued to 25 Nm (18 lb-ft) plus a 30-degree
angle.
The OM639 was produced exclusively for two vehicle
platforms during its five-year production run. The primary application was the
Smart Forfour (model designation 454), where it was marketed as the 1.5 l cdi.
This application utilized the transverse, 60-degree inclined mounting position
that the engine was specifically designed to accommodate, allowing the Forfour’s
sandwich floor structure to remain intact for crash safety. Production for the
Smart Forfour spanned from 2004 to 2006.
The second major application was the Mitsubishi Colt (model designation Z30),
where the engine was marketed under the 1.5 DI-D designation. In this
application, the engine was installed with a less pronounced inclination but
retained all core mechanical specifications. Both variants received either the
standard 70 kW (94 hp) output or, in certain markets, the reduced 50 kW (67 hp)
output for entry-level trims.
The engine was offered with both manual and automated manual transmissions
depending on the vehicle and market. Production for the Mitsubishi Colt
continued until 2009, marking the conclusion of the OM639’s manufacturing run.
No subsequent vehicles received this engine, as Mercedes-Benz transitioned to
the Renault-sourced OM607 engine family for subsequent small diesel
applications.
____________________________________________________________________________________
| Car Engines Technical Specifications |
| Small Engines Technical Specifications |
| Industrial Engines Technical Specifications |
| Outboard Engines Technical Specifications |
