Mercedes-Benz OM642 Specifications
| Engine Model: Mercedes-Benz OM642 |
| Engine Type: 4-cycle 6-cylinder DOHC 24-valve turbocharged liquid-cooled diesel |
| Total Displacement: 182.3 cu.in (2.98 L) |
| Rated Engine Power: 201-265 Hp (149-196 kW) at 3800 rpm |
| Fuel System Type: Common rail direct injection |
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The Mercedes-Benz OM642 is a 72-degree V6, dual
overhead camshaft (DOHC), 24-valve turbocharged diesel engine. This
3.0-liter common rail diesel powerplant succeeded the inline-five and
inline-six diesel engines in Mercedes-Benz's passenger car and light
truck lineup, entering production in 2005. The OM642 is constructed with
a compacted graphite iron (CGI) cylinder block and aluminum alloy
cylinder heads. It is an interference engine design.
The engine employs a third-generation common rail direct injection
system with piezoelectric injectors, variable geometry turbochargers
(single or twin, depending on variant), and a sophisticated emissions
control suite. The 72-degree V-angle allows for optimized packaging and
primary balance. The OM642 delivers high specific output, robust low-end
torque, and refined operation, though it presents specific maintenance
challenges related to its complex emission systems. It is engineered for
longitudinal and transverse mounting in a vast array of
rear-wheel-drive, all-wheel-drive, and front-wheel-drive vehicles.
General Specs
Engine Type: 72-degree V6, liquid-cooled, four-stroke, turbocharged
diesel engine with common rail injection.
Bore: 83.0 mm (3.27 in).
Stroke: 92.0 mm (3.62 in).
Displacement: 2987 cc (182.3 cu.in).
Compression Ratio: 16.2:1 (varies slightly by model year).
Firing Order: 1-4-2-5-3-6.
Cylinder Numbering: Left bank (cylinders 1-2-3) is bank 1; cylinder 1 is
at the front of this bank. Right bank (cylinders 4-5-6) is bank 2;
cylinder 4 is at the front of this bank.
Engine Rotation (viewed from the front): Clockwise.
Aspiration: Single variable geometry turbocharger (VGT) or
twin-turbocharger (Biturbo) depending on application.
Fuel Requirement: Diesel fuel conforming to EN 590 standard.
Power Output: Ranges from 201 Hp at 3400 RPM to 265 Hp at 3800 RPM for
single turbo versions; up to 325 Hp for high-performance Biturbo AMG
variants.
Torque Output: Ranges from 369 lb-ft at 1600-2400 RPM to 457 lb-ft at
1600-2400 RPM for single turbo; up to 538 lb-ft for Biturbo AMG
variants.
Maximum Engine Speed: 4600-5000 RPM.
Oil Pressure (at operating temperature): 1.0 bar (14.5 psi) minimum at
idle; 3.0-4.5 bar (44-65 psi) at 2000 RPM.
The cylinder block is manufactured from compacted graphite iron (CGI).
This material provides a higher strength-to-weight ratio and greater
stiffness than conventional grey cast iron, allowing for reduced wall
thickness and lower engine weight while withstanding high combustion
pressures. The block employs a 72-degree V-angle, optimizing packaging
and allowing for a shorter, stiffer crankshaft compared to a 60-degree
design.
The cylinder bores are machined directly into the CGI material. The
block features four main bearing caps, also made from CGI, secured with
two vertical bolts and two lateral cross-bolts per cap. The crankshaft
is a forged steel unit. Connecting rods are forged steel. Pistons are
aluminum alloy with a recessed combustion bowl and anodized top ring
lands for heat resistance. Each piston is cooled by oil jets.
Each cylinder bank is equipped with a separate aluminum alloy cylinder
head employing dual overhead camshafts (DOHC). Each head uses four
valves per cylinder, actuated via roller rocker arms (lever-type cam
followers). The camshafts are driven by a three-stage timing chain
system with hydraulic tensioners.
The valvetrain incorporates hydraulic lash adjusters integrated into the
rocker arms, eliminating manual valve clearance adjustment. The cylinder
heads incorporate integrated intake manifolds on many variants, reducing
parts count and potential for boost pressure leaks.
Valve Train Data
Valve Arrangement: DOHC, 4 valves per cylinder (24 total).
Intake Valve Head Diameter: 31.5 mm (1.24 in).
Exhaust Valve Head Diameter: 28.0 mm (1.102 in).
Valve Lash (Clearance): Hydraulic lash adjusters; no manual adjustment.
Camshaft Drive: Three-stage silent chain system (two secondary chains
from an intermediate sprocket to each camshaft, driven by a primary
chain from the crankshaft).
The fuel system is a third-generation common rail direct injection
system. Later versions employ piezoelectric inline injectors, which
offer faster and more precise multiple injection events per cycle
compared to solenoid injectors. The system uses a single-piston
high-pressure pump, driven by the left exhaust camshaft, generating rail
pressures up to 2000 bar (29,000 psi).
A fuel rail pressure sensor and control valve allow the engine control
unit (ECU) to precisely manage pressure. The system enables up to five
injection events per cycle (pre, main, and post injections) for
optimized power, noise, and emissions.
Fuel System Data
Fuel Injection Type: Common Rail Direct Injection with piezoelectric
injectors (later variants).
Injection Pressure: Up to 2000 bar (29,000 psi).
High-Pressure Pump: Single-piston radial pump, camshaft-driven.
Injector Type: Piezoelectric inline (fast-switching) or solenoid.
Glow Plarts: Quick-start ceramic glow plugs.
The lubrication system is a pressure-fed, full-flow design with a
variable-displacement vane-type oil pump. The oil pump is mounted at the
front of the engine and is chain-driven from the crankshaft. Its
displacement is controlled by engine oil pressure to reduce parasitic
losses. The system uses a replaceable cartridge-type oil filter located
in a housing on the top front of the engine.
A water-cooled oil cooler manages oil temperature. Oil is drawn from a
cast aluminum structural oil pan, pressurized, filtered, cooled, and
distributed. The system includes piston cooling jets. A critical design
note is the location of the oil cooler seals, a known failure point that
can lead to coolant-oil mixing (the "OM642 oil cooler seal issue").
Lubrication System Data
Oil Pump Type: Variable-displacement vane-type, chain-driven.
Oil Capacity (with filter change): 8.5 US quarts (8.0 liters).
Oil Filter Type: Cartridge-type paper element.
Oil Type (recommended): Mercedes-Benz approved engine oil, specification
229.51 or 229.52, 5W-30 or 0W-30 low-ash full synthetic.
Oil Change Interval: As determined by the Flexible Service System (FSS),
generally up to 10,000 miles (16,000 km) or 1 year.
The cooling system is a pressurized, dual-circuit pump-driven system. A
belt-driven mechanical water pump provides primary circulation. The
system incorporates a dual thermostat housing: a main thermostat for
engine temperature and a separate thermostat for the water-cooled oil
cooler circuit.
An electric auxiliary coolant pump operates during key-on/engine-off
situations to cool the turbocharger(s) and EGR components. The charge
air cooler is air-to-air. The EGR system uses a high-pressure loop with
a dedicated water-cooled EGR cooler.
Cooling System Data
Cooling System Type: Pressurized, pump-driven, with dual-thermostat
control.
Coolant Capacity: 14.0 US quarts (13.2 liters).
Thermostat Opening Temperature: Main thermostat opens at 87°C (189°F).
Water Pump Drive: Serpentine accessory belt.
Coolant Type: Mercedes-Benz approved coolant, usually a silicate- and
phosphate-free OAT type meeting specification 325.0.
Applications use either a single variable geometry turbocharger (VGT) or
a twin-turbo (Biturbo) setup. The Biturbo system uses two smaller turbos
(one per cylinder bank) for reduced inertia and faster response. The
turbochargers are water-cooled.
The engine employs an extensive array of emission controls. These
include Exhaust Gas Recirculation (EGR) with a cooler and valve, a
Diesel Oxidation Catalyst (DOC), and a Diesel Particulate Filter (DPF).
For NOx reduction, later BlueTEC variants add a Selective Catalytic
Reduction (SCR) system using Diesel Exhaust Fluid (AdBlue). The engine
uses multiple sensors: differential pressure sensors for the DPF, NOx
sensors, and temperature sensors.
Overall Length: 650 mm (25.6 in).
Overall Width: 750 mm (29.5 in).
Overall Height: 700 mm (27.6 in).
Approximate Dry Weight: 220 kg (485 lbs).
Engine Oil and Filter Change: Follow the Flexible Service System (FSS).
Intervals commonly extend to 10,000 miles (16,000 km) or 1 year.
Fuel Filter: Replace every 20,000 miles (32,000 km) or 2 years.
Air Filter: Replace every 40,000 miles (64,000 km) or 4 years.
Timing Chain: Not a scheduled item, but chain stretch and guide wear can
occur after 150,000 miles (240,000 km).
Diesel Particulate Filter (DPF): Regeneration occurs automatically; ash
cleaning may be required after 120,000-150,000 miles (190,000-240,000
km).
Oil Cooler Seals: Proactive inspection/replacement around 80,000-100,000
miles (130,000-160,000 km) is a common preventative measure.
Cylinder Head Bolts: Torque-to-yield. Tighten in a specific multi-stage
cross pattern with angular turns (e.g., tighten to 50 Nm / 37 lb-ft,
then +90°, then +90° again). Exact specification depends on model year.
Main Bearing Cap Bolts (vertical): 50 Nm (37 lb-ft) plus an additional
90-degree turn.
Main Bearing Cap Cross-Bolts: 50 Nm (37 lb-ft) plus an additional
90-degree turn.
Connecting Rod Cap Bolts: 30 Nm (22 lb-ft) plus an additional 90-degree
turn.
Crankshaft Damper Bolt: 300 Nm (221 lb-ft) plus an additional 90-degree
turn.
Camshaft Sprocket Bolts: 60 Nm (44 lb-ft).
High-Pressure Pump Sprocket Bolt: 60 Nm (44 lb-ft).
Fuel Injector Hold-Down Clamp Bolt: 12 Nm (9 lb-ft).
Oil Pan Drain Plug: 30 Nm (22 lb-ft).
Oil Filter Housing Cap: 25 Nm (18 lb-ft).
The Mercedes-Benz OM642 engine has been
installed in an extensive range of models:
Mercedes-Benz C-Class (W204, C300 CDI, C350 CDI).
Mercedes-Benz E-Class (W211, W212, E320 CDI, E350 CDI, E350 BlueTEC).
Mercedes-Benz S-Class (W221, S320 CDI, S350 CDI).
Mercedes-Benz GLK-Class (X204, GLK320 CDI, GLK350 CDI).
Mercedes-Benz M-Class (W164, ML320 CDI, ML350 CDI, ML350 BlueTEC).
Mercedes-Benz GL-Class (X164, GL320 CDI, GL350 CDI).
Mercedes-Benz R-Class (W251, R320 CDI, R350 CDI).
Mercedes-Benz Sprinter (NCV3, 3.0L V6).
Jeep Grand Cherokee (WK2, 3.0L CRD).
Chrysler 300 (LD, 3.0L CRD).
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