Mercedes-Benz M256 Specifications
| Engine Model: Mercedes-Benz M256 |
| Engine Type: 4-cycle inline 6-cylinder DOHC 24-valve liquid-cooled gasoline |
| Total Displacement: 183 cu.in (2.99 L) |
| Rated Engine Power: 362-435 Hp (268-322 kW) at 6100 rpm |
| Fuel System Type: Gasoline direct injection (GDI) |
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The Mercedes-Benz M256 is an inline-six
cylinder, double overhead camshaft (DOHC), 24-valve gasoline engine with
an integrated electric motor. This 3.0-liter engine is a member of
Mercedes-Benz's modular family of gasoline engines and represents a
fundamental shift in powertrain philosophy, incorporating a 48-volt
electrical system for hybridization. Production commenced in 2017 and
continues. The M256 is a mild-hybrid engine, featuring an Integrated
Starter Generator (ISG) mounted between the engine and transmission, a
belt-driven starter generator for the 12V system, and an electric
auxiliary compressor (eZV).
It is an all-aluminum engine with a closed-deck block and spray-coated
cylinder liners (Nanoslide). This engine is an interference design. The
M256 combines turbocharging, direct fuel injection, and sophisticated
electrification to deliver high power and torque with improved
efficiency and reduced turbo lag. It is engineered for longitudinal
mounting in rear-wheel-drive and all-wheel-drive luxury sedans, coupes,
and SUVs.
Engine Type: Inline-six cylinder, liquid-cooled, four-stroke,
turbocharged and electrically assisted gasoline engine with 48V
mild-hybrid system.
Bore: 83.0 mm (3.27 in).
Stroke: 92.4 mm (3.64 in).
Displacement: 2999 cc (183.0 cu.in).
Compression Ratio: 10.5:1 (varies slightly by specific variant).
Firing Order: 1-5-3-6-2-4.
Cylinder Numbering: Number 1 cylinder is at the accessory drive (front)
end.
Engine Rotation (viewed from the front): Clockwise.
Fuel Requirement: Premium unleaded gasoline, 91 pump octane (RON 95)
minimum; higher octane recommended for maximum performance.
Power Output: Ranges from 362 Hp at 5500-6100 RPM to 435 Hp at 6100 RPM
(268-322 kW), depending on application and tune (engine only, excluding
ISG boost).
Torque Output: Ranges from 369 lb-ft at 1600-4000 RPM to 384 lb-ft at
1800-5800 RPM, depending on application (engine only). The ISG can
provide an additional 184 lb-ft of transient torque.
Maximum Engine Speed: 6100-6500 RPM (fuel cut-off).
System Voltage: Primary 48V architecture with a separate 12V system.
The cylinder block is a high-pressure die-cast aluminum alloy using a
closed-deck design. This configuration provides maximum rigidity for
high combustion pressures. It employs the Nanoslide cylinder coating
process, where an iron/carbon wire is melted in an electric arc and
sprayed onto the aluminum bore surface, then honed to an ultra-smooth,
mirror-like finish.
This coating replaces conventional cast iron liners, reducing weight and
improving heat dissipation. The block features a deep-skirt
construction. The crankshaft is a forged steel unit with seven main
bearings. Connecting rods are forged steel. Pistons are cast aluminum
alloy with cooling channels supplied by dedicated oil jets. The pistons
feature a specially shaped crown to optimize combustion with direct
injection.
The cylinder head is an aluminum alloy casting employing dual overhead
camshafts (DOHC). It features a central direct fuel injector and a
side-mounted spark plug per cylinder. The intake and exhaust camshafts
are equipped with continuous variable valve timing (VVT). The valvetrain
uses a direct-acting design with roller-finger followers and hydraulic
lash adjusters, eliminating manual valve clearance adjustment. The
camshafts are driven by a maintenance-free two-stage chain system with
hydraulic tensioners.
Valve Arrangement: DOHC, 4 valves per cylinder (24 total).
Intake Valve Head Diameter: 30.0 mm (1.181 in).
Exhaust Valve Head Diameter: 26.0 mm (1.024 in).
Valve Stem Diameter: 5.0 mm (0.197 in).
Valve Lash (Clearance): Hydraulic lash adjusters; no manual adjustment.
Camshaft Drive: Two-stage silent chain with hydraulic tensioners and
guide rails.
Camshaft Adjustment: Continuous variable timing on intake and exhaust
camshafts.
The fuel system is a direct-injection system operating at high pressure.
It uses a camshaft-driven, single-piston high-pressure fuel pump mounted
on the cylinder head. Fuel rails supply six solenoid-actuated,
multi-hole injectors positioned centrally in the combustion chamber.
The low-pressure supply is provided by an in-tank electric fuel pump.
The system incorporates a returnless fuel circuit. The engine control
unit (ECU) precisely controls injection timing and multiple injection
events per cycle for optimized power, efficiency, and emissions.
Fuel Injection Type: Gasoline Direct Injection (GDI).
High-Pressure Fuel Pump Pressure: Up to 250 bar (3625 psi).
Low-Pressure Supply Pressure: 5.0 bar (72.5 psi).
Injector Type: Solenoid-actuated, multi-hole.
Ignition System: Coil-on-plug with individual ignition coils.
The lubrication system is a pressure-fed, variable-displacement design.
A vane-type, variable-displacement oil pump is mounted at the front of
the engine and is chain-driven from the crankshaft. The pump adjusts its
output based on engine demand to reduce parasitic losses.
The system uses a cartridge-type oil filter located in a housing on the
engine. A water-cooled oil cooler manages oil temperature. The system
includes piston cooling jets. Oil passages feed the crankshaft and
connecting rod bearings, camshaft phasers and journals, timing chain
tensioners, and the turbocharger center section.
Oil Pump Type: Variable-displacement vane-type, 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
229.61 or 229.71, 0W-20 full synthetic low-ash oil.
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, complex pump-driven system with
multiple circuits. A belt-driven mechanical water pump provides primary
circulation for the engine block and head. The system includes a
separate electric coolant pump for the turbocharger and the 48V
Integrated Starter Generator (ISG) to provide cooling independent of
engine speed, including after shutdown.
A thermostatic map-controlled thermostat regulates coolant temperature,
opening at approximately 105°C (221°F) under normal load for improved
efficiency. The intercooler for the turbocharger is integrated into the
intake manifold (water-to-air intercooler).
Cooling System Type: Pressurized, pump-driven, with map-controlled
thermostat and auxiliary electric pumps.
Coolant Capacity: Approximately 11.0 US quarts (10.4 liters).
Thermostat Opening Temperature: Map-controlled, nominal 105°C (221°F).
Water Pump Drive: Serpentine accessory belt (main pump).
Coolant Type: Mercedes-Benz antifreeze mixture, usually a silicate- and
phosphate-free OAT type meeting specification 325.0.
| 48V Mild-Hybrid System (EQ Boost) |
The core electrification feature is the 48V system. An Integrated
Starter Generator (ISG), a disc-shaped electric motor, is mounted
between the engine and transmission. It serves multiple functions:
providing up to 21 Hp and 184 lb-ft of torque for short bursts (e.g.,
for acceleration assist or to fill torque gaps during turbo spool-up),
enabling seamless start-stop operation, generating electricity via
recuperation during braking, and allowing for brief "gliding" with the
engine off. A separate belt-driven starter generator (RSG) maintains the
12V electrical system.
The engine employs a single twin-scroll turbocharger. A key innovation
is the electric auxiliary compressor (eZV). This electrically driven
compressor, operating on the 48V system, provides immediate boost
pressure at low engine speeds before the exhaust-driven turbocharger
reaches operating speed, effectively eliminating turbo lag. The
compressor is mounted in the intake tract upstream of the main
turbocharger.
Overall Length (engine only, without ISG): 580 mm (22.8 in).
Overall Width: 700 mm (27.6 in).
Overall Height: 660 mm (26.0 in).
Approximate Dry Weight (engine including ISG): 198 kg (437 lbs).
Engine Oil and Filter Change: Follow the Flexible Service System (FSS)
in the instrument cluster. Intervals are condition-based but generally
reach up to 10,000 miles (16,000 km) or 1 year. Spark Plugs: Replace
every 62,000 miles (100,000 km) or 6 years. Air Filters: Replace every
37,500 miles (60,000 km). Fuel Filter: Integrated into the fuel pump
module; replacement is part of a module service, not a standalone item.
Coolant: First replacement at 15 years or 180,000 miles (290,000 km),
then every 5 years thereafter. Accessory Drive Belts: Inspect every
20,000 miles (32,000 km); the belt for the RSG has a specific
replacement interval (e.g., 75,000 miles / 120,000 km). Timing Chain:
Designed for the operational life of the engine; not a scheduled
maintenance item.
Cylinder Head Bolts: Torque-to-yield bolts tightened in multiple stages
with specific angle turns according to the official repair
documentation. A general sequence involves preliminary torque plus
multiple angular turns (e.g., 90° + 90°).
Main Bearing Cap Bolts: Torque-to-yield bolts tightened with a final
angular turn specification.
Connecting Rod Cap Bolts: Torque-to-yield bolts, tightened to a final
torque plus an angular turn (e.g., 30 Nm / 22 lb-ft + 90°).
Crankshaft Damper Bolt: 200 Nm (148 lb-ft) plus an additional 90-degree
turn.
Camshaft Adjuster Sprocket Bolt: 60 Nm (44 lb-ft) plus an additional
90-degree turn.
Spark Plugs: 25 Nm (18 lb-ft).
Oil Pan Drain Plug: 30 Nm (22 lb-ft).
Oil Filter Housing Cap: 25 Nm (18 lb-ft).
The Mercedes-Benz M256 engine is installed
in numerous current-generation models, including:
Mercedes-Benz S-Class (W222/V223, S450, S500).
Mercedes-Benz C-Class (W205/S206, C450 AMG, C43 AMG - later versions).
Mercedes-Benz E-Class (W213/S213, E450, E53 AMG).
Mercedes-Benz CLS (C257, CLS450, CLS53 AMG).
Mercedes-Benz GLE (W167, GLE450).
Mercedes-Benz GLS (X167, GLS450).
Mercedes-Benz GLC (X253/C253, GLC43 AMG - later versions).
Mercedes-Benz GT 4-Door Coupe (X290, GT 53 AMG).
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