Mercedes-Benz M112 Specifications
| Engine Model: Mercedes-Benz M112 |
| Engine Type: 4-cycle 6-cylinder SOHC 18-valve liquid-cooled gasoline |
| Total Displacement: 195.2 cu.in (3.19 L) |
| Rated Engine Power: 218-245 Hp (161-181 kW) at 5700 rpm |
| Fuel System Type: Sequential multi-point electronic fuel injection (SFI) |
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The Mercedes-Benz M112 is a 90-degree V6,
single overhead camshaft (SOHC), 18-valve gasoline engine. This engine
family, with displacements of 2.8 liters, 3.2 liters, and 3.7 liters,
was produced from 1997 through 2006. The M112 represents a significant
modernization in Mercedes-Benz's engine technology, introducing an
all-aluminum construction with cast-in silicon-aluminum cylinder liners
(Silitec), a three-valve-per-cylinder design, and twin-spark ignition.
It is an interference engine design.
The M112 was engineered as a replacement for the older M104 inline-six
cylinder engines, offering improved packaging, reduced weight, and lower
fuel consumption while maintaining Mercedes-Benz standards of smoothness
and durability. The engine employs a structural aluminum oil pan and a
duplex chain-driven valvetrain. It was used in a wide array of
Mercedes-Benz passenger cars, from sedans and coupes to SUVs, in both
rear-wheel-drive and all-wheel-drive configurations.
Engine Type: 90-degree V6, liquid-cooled, four-stroke gasoline engine.
Bore: 89.9 mm (3.54 in).
Stroke: 84.0 mm (3.31 in) for 3.2L; 92.8 mm (3.65 in) for 3.7L.
Displacement: 3199 cc (195.2 cu.in) for M112 E32; 3724 cc (227.3 cu.in)
for M112 E37.
Compression Ratio: 10.0:1.
Firing Order: 1-4-3-6-2-5.
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.
Engine Rotation (viewed from the front): Clockwise.
Fuel Requirement: Premium unleaded gasoline, 91 pump octane (RON 95)
minimum.
Power Output (M112 E32): 218 Hp (161 kW) at 5700 RPM.
Power Output (M112 E37): 245 Hp (181 kW) at 5700 RPM.
Torque Output (M112 E32): 229 lb-ft at 3000-4600 RPM.
Torque Output (M112 E37): 254 lb-ft at 3000-4500 RPM.
Maximum Engine Speed: 6000 RPM.
Oil Pressure (at operating temperature): 1.0 bar (14.5 psi) minimum at
idle speed; 3.5-4.5 bar (51-65 psi) at 3000 RPM.
The cylinder block is a high-pressure die-cast aluminum alloy
(AlSi17Cu4Mg) with a closed-deck design for high rigidity. It employs
cast-in silicon-aluminum cylinder liners using the "Silitec" process,
where the hypereutectic aluminum alloy of the liner is integral to the
block casting, providing excellent heat dissipation and wear resistance
without separate iron liners. The block features a deep-skirt
construction.
The crankshaft is a forged steel unit with four main bearings. The main
bearing caps are cast iron and are cross-bolted (with lateral bolts) for
added strength. Connecting rods are forged steel. Pistons are aluminum
alloy with a graphite-coated skirt for reduced friction. Each piston
uses two compression rings and one oil control ring.
Each cylinder bank is equipped with a separate aluminum alloy cylinder
head. The cylinder heads employ a single overhead camshaft (SOHC) per
bank, operating a three-valve-per-cylinder layout: two intake valves and
one large exhaust valve.
The valvetrain uses roller rocker arms with hydraulic lash adjusters,
eliminating manual valve clearance adjustment. The camshafts are driven
by a two-stage duplex roller chain system from the crankshaft. A key
feature is the twin-spark ignition system, with two spark plugs per
cylinder located on opposite sides of the combustion chamber.
Valve Arrangement: SOHC, 3 valves per cylinder (18 total).
Intake Valve Head Diameter: 34.5 mm (1.358 in).
Exhaust Valve Head Diameter: 39.0 mm (1.535 in).
Valve Stem Diameter: 6.0 mm (0.236 in).
Valve Lash (Clearance): Hydraulic lash adjusters; no manual adjustment.
Camshaft Drive: Duplex roller chain with hydraulic tensioners and
mechanical guides.
The fuel system is a sequential multi-port electronic fuel injection
(SFI) system, known by Mercedes-Benz as "CIS-E" (Continuous Injection
System-Electronic) in early versions and "ME-SFI"
(Motor-Elektronik-Sequential Fuel Injection) in later versions. The
system is a returnless design.
Components include two in-tank electric fuel pumps (primary and
booster), a fuel filter, a fuel rail, and six injectors. Fuel pressure
is regulated by a pressure control valve in the fuel filter housing. The
system is managed by a sophisticated engine control unit that integrates
the ignition and fuel delivery.
Fuel Injection Type: Sequential Multi-Port Fuel Injection (SFI).
Fuel Pressure (at rail, static): 3.8 bar (55 psi) with key on/engine
off.
Injector Flow Rate: Approximately 180 cc/min at 3.0 bar.
Idle Speed Control: Managed by the engine control unit via the
electronic throttle actuator (ETC).
Idle Speed (base, in neutral): 650 ± 50 RPM.
The lubrication system is a pressure-fed, full-flow design with a
gear-type oil pump. The oil pump is mounted externally on the front of
the engine block and is driven by a chain from the crankshaft. The
system incorporates a replaceable cartridge-type paper oil filter
located in a housing on the front of the cylinder block. Oil is drawn
from a structural cast aluminum oil pan, which contributes to engine
block stiffness.
The oil pan includes internal baffles. Oil is pressurized, filtered, and
distributed through main galleries. The system includes piston cooling
jets. The oil filter housing contains the main oil pressure relief valve
and an oil cooler thermostat that directs oil to a water-cooled oil
cooler once operating temperature is reached.
Oil Pump Type: Gear-type, chain-driven.
Oil Capacity (with filter change): 7.0 US quarts (6.6 liters).
Oil Capacity (dry fill): 8.0 US quarts (7.6 liters).
Oil Filter Type: Cartridge-type paper element.
Oil Type (recommended): Mercedes-Benz approval 229.3 or 229.5, 0W-40 or
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. An impeller-type water pump, driven by the
serpentine accessory belt, provides circulation. The system uses a
dual-circuit thermostat. The primary thermostat opens at 87°C (189°F),
allowing coolant to flow to the radiator.
The engine management system can also activate an electrically heated
map thermostat to open earlier under certain load conditions for optimal
thermal management. Coolant flows through the block, cylinder heads, and
a water-cooled oil heat exchanger. The system includes a plastic
expansion tank with integrated coolant level sensor.
Cooling System Type: Pressurized, pump-driven, with dual-circuit
thermostatic control.
Coolant Capacity: 11.5 US quarts (10.9 liters).
Thermostat Opening Temperature: Primary stage at 87°C (189°F).
Radiator Cap Pressure Rating: 1.4 bar (20 psi).
Water Pump Drive: Serpentine accessory belt.
Coolant Type: Mercedes-Benz antifreeze mixture (Glysantin G48 or
equivalent, silicate-based), mixed 50/50 with deionized water.
The ignition system is a distributorless, coil-per-cylinder design with
twin-spark capability. Six individual ignition coils, each serving one
cylinder, fire two spark plugs per cylinder simultaneously. The engine
control unit controls each coil independently.
This twin-spark design promotes more complete combustion and allows for
a large single exhaust valve. Spark plugs are platinum-tipped with a
long service interval. The system uses two knock sensors (one per bank).
| Electronic Throttle Control |
The engine uses a drive-by-wire electronic throttle control (ETC)
system, known as "EGAS." The accelerator pedal position sensor sends a
signal to the engine control unit, which commands the electric motor on
the throttle body. This system integrates cruise control, traction
control, and idle speed functions.
Overall Length: 650 mm (25.6 in).
Overall Width: 750 mm (29.5 in).
Overall Height: 700 mm (27.6 in).
Approximate Dry Weight: 185 kg (408 lbs).
Service Intervals:
Engine Oil and Filter Change: Every 10,000 miles (16,000 km) or 1 year,
whichever comes first.
Spark Plugs: Replace every 60,000 miles (96,000 km) for long-life
platinum plugs.
Air Filter: Replace every 40,000 miles (64,000 km) or 4 years.
Fuel Filter: Replace every 40,000 miles (64,000 km).
Coolant: Replace every 15 years or 150,000 miles (240,000 km) for
original G48 coolant.
Accessory Drive Belt: Inspect every 20,000 miles (32,000 km); replace if
cracked or glazed.
Timing Chain: Not a scheduled maintenance item; designed for the
engine's operational life.
Fluids and Filters:
Engine Oil Grade: Full synthetic meeting MB 229.3 or 229.5
specification.
Coolant Type: Mercedes-Benz approved silicate-based antifreeze (G48).
Transmission Fluid: Specific Mercedes-Benz ATF (e.g., 236.10 or 236.12)
for attached automatic transmissions.
Cylinder Head Bolts (M11): Tighten in three stages using a specific
cross pattern. Final torque is 40 Nm (30 lb-ft) plus an additional
90-degree turn.
Main Bearing Cap Bolts (vertical): 30 Nm (22 lb-ft) plus an additional
90-degree turn.
Main Bearing Cap Cross-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: 300 Nm (221 lb-ft) plus an additional 90-degree
turn.
Camshaft Sprocket Bolt: 70 Nm (52 lb-ft).
Spark Plugs: 25 Nm (18 lb-ft).
Oil Pan Drain Plug: 35 Nm (26 lb-ft).
Oil Filter Housing Cap: 25 Nm (18 lb-ft).
The Mercedes-Benz M112 engine was installed
in numerous models, including:
Mercedes-Benz C-Class (W203, C320).
Mercedes-Benz CLK-Class (W208, CLK320).
Mercedes-Benz E-Class (W210, E320; W211, E320).
Mercedes-Benz S-Class (W220, S320, S350).
Mercedes-Benz SL-Class (R230, SL350).
Mercedes-Benz CL-Class (W215, CL500 - early models used M113 V8, but
related).
Mercedes-Benz M-Class (W163, ML320, ML350).
Mercedes-Benz G-Class (W463, G500 - early models used M113 V8, but
related).
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