Mercedes-Benz OM612 Specifications
| Engine Model: Mercedes-Benz OM612 |
| Engine Type: 4-cycle inline 5-cylinder DOHC 20-valve turbocharged liquid-cooled diesel |
| Total Displacement: 163.8 cu.in (2.68 L) |
| Rated Engine Power: 161-170 Hp (120-126 kW) at 4200 rpm |
| Fuel System Type: Common rail direct injection |
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The Mercedes-Benz OM612 is an inline-five
cylinder, dual overhead camshaft (DOHC), 20-valve turbocharged diesel
engine. This 2.7-liter common rail diesel powerplant was the first of
Mercedes-Benz's modern generation of passenger car diesel engines,
introduced in 1997. Production continued through the mid-2000s. The
OM612 engine is constructed with a cast-iron cylinder block and an
aluminum cylinder head. It is an interference engine design. A defining
technological feature is its second-generation common rail direct
injection system, which operates at high pressure for refined
performance and reduced emissions.
The engine employs a variable geometry turbocharger (VGT) for broad
torque delivery and incorporates four valves per cylinder. The OM612
delivers strong low-end torque, respectable fuel economy, and a
significant step forward in diesel refinement for passenger vehicles. It
was engineered for longitudinal mounting in rear-wheel-drive and
all-wheel-drive platforms, serving as a cornerstone for Mercedes-Benz
diesel offerings in sedans, wagons, and SUVs.
Engine Type: Inline-five cylinder, liquid-cooled, four-stroke,
turbocharged diesel engine with common rail injection.
Bore: 88.0 mm (3.46 in).
Stroke: 88.0 mm (3.46 in).
Displacement: 2685 cc (163.8 cu.in).
Compression Ratio: 18.0:1.
Firing Order: 1-2-4-5-3.
Cylinder Numbering: Number 1 cylinder is at the accessory drive (front)
end.
Engine Rotation (viewed from the front): Clockwise.
Aspiration: Variable Geometry Turbocharger (VGT).
Fuel Requirement: Diesel fuel conforming to EN 590 standard.
Power Output: Ranges from 161 Hp at 4200 RPM to 170 Hp at 4200 RPM
(120-126 kW).
Torque Output: Ranges from 273 lb-ft at 1800-2400 RPM to 295 lb-ft at
1600-2400 RPM, depending on application.
Maximum Engine Speed: 4800 RPM.
Oil Pressure (at operating temperature): 1.0 bar (14.5 psi) minimum at
idle; 2.5-4.5 bar (36-65 psi) at 2000 RPM.
The cylinder block is manufactured from cast iron using a grey iron
alloy. It is a rigid design with a deep-skirt configuration that
contributes to overall engine stiffness and noise reduction. The
cylinder bores are machined directly into the block material. The block
incorporates six main bearing saddles to support the five-cylinder
crankshaft, providing enhanced stability.
The main bearing caps are made from cast iron and are secured with two
vertical bolts each. The crankshaft is a forged steel unit with
counterweights designed to balance the inherent vibrations of a
five-cylinder layout. Connecting rods are forged steel. Pistons are
aluminum alloy with a recessed combustion bowl in the crown, optimized
for the direct injection combustion process. Each piston uses three
rings.
The cylinder head is an aluminum alloy casting employing dual overhead
camshafts (DOHC). It uses a cross-flow design with four valves per
cylinder. The camshafts are driven by a single-stage timing chain with
hydraulic tensioners. The valve train uses a direct-acting design with
mechanical bucket tappets.
Valve clearance is adjusted using select-fit shims located between the
camshaft lobe and the top of the tappet. The cylinder head integrates
the intake ports and houses the injectors and glow plugs.
Valve Arrangement: DOHC, 4 valves per cylinder (20 total).
Intake Valve Head Diameter: 30.5 mm (1.201 in).
Exhaust Valve Head Diameter: 27.5 mm (1.083 in).
Valve Stem Diameter: 6.0 mm (0.236 in).
Valve Lash (Clearance): Mechanical buckets with select-fit shims.
Clearance is 0.15-0.25 mm (0.006-0.010 in) for intake, 0.30-0.40 mm
(0.012-0.016 in) for exhaust, checked cold.
Camshaft Drive: Single-stage roller chain with hydraulic tensioner and
guide rails.
The fuel system is a second-generation common rail direct injection
system. The system comprises a high-pressure fuel pump driven by the
exhaust camshaft, a common fuel rail (accumulator), and five
solenoid-controlled injectors.
The system operates at high pressure, with the engine control unit (CDI
control unit) managing injection timing, duration, and in later
versions, pilot injection for noise reduction. A fuel temperature sensor
and a rail pressure sensor provide critical feedback for control. A
pre-supply pump in the fuel tank delivers fuel to the high-pressure
pump.
Fuel Injection Type: Common Rail Direct Injection.
Injection Pressure: Up to 1350 bar (19,580 psi).
High-Pressure Pump: Radial piston pump, camshaft-driven.
Injector Type: Solenoid-actuated, multi-hole.
Glow Plugs: Ceramic or steel glow plugs for cold starting assistance.
The lubrication system is a pressure-fed, full-flow design with a
rotor-type oil pump. The oil pump is mounted at the front of the engine
and is chain-driven from the crankshaft. The system uses a replaceable
cartridge-type oil filter located in a housing on the side of the
cylinder block. An oil cooler, integrated into the engine's coolant
circuit, manages oil temperature.
Oil is drawn from a stamped steel oil pan, pressurized, filtered, and
distributed through main galleries. The system includes piston cooling
jets which spray oil onto the underside of each piston. Oil passages
feed the crankshaft and connecting rod bearings, camshaft bearings,
timing chain tensioner, and the variable geometry turbocharger actuator.
Oil Pump Type: Rotor-type (gerotor), chain-driven.
Oil Capacity (with filter change): 7.4 US quarts (7.0 liters).
Oil Filter Type: Cartridge-type paper element.
Oil Type (recommended): Mercedes-Benz approved engine oil, specification
229.3 or 229.5, 5W-40 full synthetic.
Oil Change Interval: 10,000 miles (16,000 km) or 1 year under normal
service conditions.
The cooling system is a pressurized, pump-driven system with an aluminum
crossflow radiator. A belt-driven centrifugal water pump provides
circulation. The system uses a wax-pellet thermostat that opens at 87°C
(189°F). Coolant flows through the block, cylinder head, oil cooler, and
EGR cooler.
An electric auxiliary coolant pump may operate after engine shutdown to
circulate coolant through the turbocharger and EGR cooler to mitigate
heat soak. The charge air cooler (intercooler) is air-to-air and
separate from the engine coolant circuit.
Cooling System Type: Pressurized, pump-driven, with thermostatic
control.
Coolant Capacity: 11.0 US quarts (10.4 liters).
Thermostat Opening Temperature: 87°C (189°F).
Water Pump Drive: Serpentine accessory belt.
Coolant Type: Mercedes-Benz antifreeze mixture (Glysantin G48 or
equivalent, silicate-based), mixed 50/50 with deionized water.
| Turbocharging and Emission Control |
The engine employs a variable geometry turbocharger (VGT) with
electronically controlled guide vanes. This allows for optimal boost
characteristics across the engine speed range, reducing turbo lag and
improving low-end torque.
Emission control systems include an Exhaust Gas Recirculation (EGR)
system with a cooler to reduce NOx emissions, a closed crankcase
ventilation system, and an oxidation catalytic converter. The engine
management system is designated CDI (Common Rail Direct Injection).
The CDI engine control unit integrates control of the high-pressure
pump, injectors, VGT actuator, EGR valve, and glow plug system. It uses
data from numerous sensors including rail pressure, boost pressure, mass
airflow, and coolant temperature.
Overall Length: 720 mm (28.3 in).
Overall Width: 650 mm (25.6 in).
Overall Height: 700 mm (27.6 in).
Approximate Dry Weight: 205 kg (452 lbs).
Engine Oil and Filter Change: Every 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 maintenance item; designed for the
engine's operational life. Inspection for stretch or guide wear is
advised after 150,000 miles (240,000 km).
Valve Clearance Adjustment: Check every 60,000 miles (96,000 km); adjust
as necessary by replacing shims.
Glow Plugs: Test as part of routine maintenance; replace as needed.
Cylinder Head Bolts: Torque-to-yield bolts. Tighten in a specific
multi-stage cross pattern. Final stage involves a 90-degree angular
turn. Exact initial torque values (e.g., 40 Nm / 30 lb-ft) plus angle
turns must follow manufacturer sequence.
Main Bearing Cap Bolts: 30 Nm (22 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: 200 Nm (148 lb-ft) plus an additional 90-degree
turn.
Camshaft Sprocket Bolts: 55 Nm (41 lb-ft).
Fuel Injector Hold-Down Clamp Bolt: 12 Nm (9 lb-ft).
High-Pressure Pump Sprocket Bolt: 60 Nm (44 lb-ft).
Spark Plugs (Glow Plugs): 15 Nm (11 lb-ft).
Oil Pan Drain Plug: 30 Nm (22 lb-ft).
Oil Filter Housing Cap: 25 Nm (18 lb-ft).
The OM612 engine was installed in the
following passenger and light commercial vehicles:
Mercedes-Benz C-Class (W203, C270 CDI).
Mercedes-Benz E-Class (W210, E270 CDI; W211, E270 CDI).
Mercedes-Benz S-Class (W220, S270 CDI – certain markets).
Mercedes-Benz CLK-Class (W209, CLK270 CDI).
Mercedes-Benz SLK-Class (R171, SLK280 CDI – later OM642).
Mercedes-Benz M-Class (W163, ML270 CDI).
Mercedes-Benz Sprinter (903 series, 2.7 CDI).
Mercedes-Benz Vito (639 series, 2.7 CDI).
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