Mitsubishi 6M70 Specifications
| Engine Model: Mitsubishi 6M70 |
| Engine Type: 4-cycle inline 6-cylinder OHC 24-valve turbocharged liquid-cooled diesel |
| Total Displacement: 786 cu.in (12.9 L) |
| Rated Engine Power: 350-520 Hp (257-382 kW) at 2000 rpm |
| Fuel System Type: Common rail direct injection |
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The Mitsubishi 6M70 is a 12.9-liter, heavy-duty inline
six-cylinder diesel engine that succeeded the 6D40 series as the primary
powerplant for the Mitsubishi Fuso Super Great trucks and heavy-duty buses.
Developed during the early 2000s, this engine represented a significant
technological leap for Mitsubishi Fuso, incorporating an overhead camshaft (OHC)
valvetrain, four-valve-per-cylinder architecture, and common rail direct
injection to meet increasingly stringent emissions regulations while improving
power density and fuel efficiency.
The 6M70 was engineered for the demanding requirements of long-haul
transportation, construction logistics, and passenger transport, where
reliability under sustained high load is paramount. Its inline six-cylinder
configuration provides inherent primary and secondary balance, eliminating the
need for balance shafts and contributing to the engine’s smooth operation across
its operating range.
The introduction of a variable geometry turbocharger (VGT) on later variants
allowed for optimized boost delivery across the entire rpm spectrum, reducing
turbo lag and enhancing drivability in urban and highway environments.
Throughout its production life, the 6M70 became synonymous with Mitsubishi
Fuso’s heavy-duty offerings, valued for its combination of robust construction,
serviceability, and competitive performance metrics in the Japanese and export
markets.
The 6M70 is a four-stroke, water-cooled diesel engine operating on the
compression-ignition principle. The engine architecture is an inline
six-cylinder configuration with a displacement of 12.882 liters (786 cu.in),
derived from a bore of 135 mm (5.31 in) and a stroke of 150 mm (5.91 in). This
under-square design, with stroke exceeding bore, is characteristic of heavy-duty
diesel engines, promoting high torque generation at low crankshaft speeds and
enhancing thermal efficiency. The compression ratio is set at 17.0:1 across the
majority of variants, a value that balances cold-start capability with the
combustion pressures generated by the common rail fuel system.
The valvetrain utilizes a single overhead camshaft (OHC) arrangement driven by
gears at the front of the engine, a configuration that eliminates timing chains
or belts and provides exceptional durability. Four valves per cylinder - two
intake and two exhaust - are actuated via roller rocker arms with integrated
hydraulic lash adjusters, removing the need for periodic valve clearance
adjustments.
The firing order for this inline six-cylinder engine is 1-5-3-6-2-4, ensuring
even firing intervals of 120 degrees of crankshaft rotation. The rated speed is
governed at 2,000 rpm, with maximum power and torque peaks occurring within this
range to preserve longevity. Idling speed is set between 500 rpm and 600 rpm
depending on application and transmission configuration.
Performance outputs vary by T-code and application. Standard power ratings range
from 257 kW (350 hp) to 382 kW (520 hp) at 2,000 rpm. Torque characteristics are
the defining feature of the 6M70, with peak torque figures ranging from 1,620 Nm
(1,195 lb-ft) in standard configurations to 2,160 Nm (1,593 lb-ft) in
high-output variants. Maximum torque is achieved at 1,100 rpm, a low engine
speed that enables superior gradeability and reduced transmission shifting in
fully loaded conditions.
The cylinder block is manufactured from gray cast iron
with a deep-skirt design, extending below the crankshaft centerline to provide
exceptional structural rigidity. This construction minimizes bore distortion
under high cylinder pressures and reduces noise, vibration, and harshness. The
crankcase features a closed-deck design, where the area surrounding the cylinder
bores is a solid casting, enhancing the structural support for the cylinder
liners. The engine utilizes replaceable wet-type cylinder liners manufactured
from centrifugally cast iron.
These liners are in direct contact with the engine coolant, providing superior
heat dissipation from the combustion chamber. The liner protrusion above the
block deck is precisely controlled to ensure a high-integrity seal when the
cylinder head is torqued. The main bearing caps are constructed from
high-strength nodular cast iron and are secured with vertical bolts through the
cap into the block. The cylinder block incorporates an integrated gear train
housing at the front end, which houses the camshaft drive gears, injection pump
drive gear, and accessory drives, contributing to the engine’s compact overall
length.
The cylinder head is a single casting manufactured from
gray cast iron, covering all six cylinders in a monolithic structure. This
design provides maximum rigidity and simplifies the sealing interface with the
cylinder block. The overhead camshaft (OHC) arrangement positions the camshaft
directly above the valves, reducing the number of moving components compared to
pushrod designs and enabling higher engine speeds with greater valvetrain
stability. The camshaft is supported by five bearing journals and is driven by a
gear train at the front of the engine.
Each cylinder utilizes four valves - two intake and two exhaust - arranged in a
cross-flow configuration that optimizes volumetric efficiency and combustion
chamber swirl characteristics. The valves are actuated by roller rocker arms
that incorporate hydraulic lash adjusters, eliminating the need for manual valve
clearance adjustments throughout the engine’s service life.
The exhaust valves are equipped with sodium cooling; the hollow stems are
partially filled with sodium which liquefies at operating temperature and
transfers heat from the valve head to the stem and into the valve guide. Valve
seat inserts are constructed from high-cobalt alloys to withstand the thermal
and mechanical stresses of turbocharged operation with exhaust gas
recirculation. 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 6M70 is equipped with a third-generation common
rail fuel injection system. A high-pressure pump, driven by the front gear
train, supplies fuel to the common rail accumulator at pressures reaching 1,600
bar (23,206 psi). The rail distributes pressurized fuel to electronically
controlled injectors positioned centrally within each cylinder. These injectors
utilize solenoid actuation and are capable of multiple injection events per
combustion cycle, including pilot injection, main injection, and post-injection.
Pilot injection reduces combustion noise and improves cold-start behavior by
pre-heating the combustion chamber.
Post-injection raises exhaust gas temperatures to facilitate regeneration of the
diesel particulate filter and selective catalytic reduction system. The fuel
system is managed by an electronic control unit that monitors crankshaft
position, camshaft position, accelerator pedal position, boost pressure, intake
air temperature, and fuel rail pressure to calculate injection timing and
duration with precision. The fuel filtration system incorporates a water
separator, a pre-filter, and a main 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 mounted at the front of the
engine and driven by the gear train. The oil pump draws lubricant from the sump
through a strainer and delivers it to the main oil gallery. The system maintains
stable oil pressure across the operating range, with a pressure relief valve
calibrated to maintain pressure between 3.5 bar and 5.0 bar (51 psi to 73 psi)
at operating speed. A large-capacity oil cooler, of the plate-and-fin type, is
integrated into the engine coolant circuit and mounted on the side of the
cylinder block.
This configuration maintains oil viscosity under sustained high-load conditions
such as long-haul trucking or mountainous operation. The engine employs a
full-flow spin-on oil filter with an integral bypass valve. The oil pan capacity
varies by vehicle application, ranging from 31 liters (8.2 US gal) to 36 liters
(9.5 US gal) depending on the oil pan depth and the presence of an oil cooler
circuit. An oil level sensor is integrated into the sump to provide real-time
monitoring to the instrument cluster.
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 80°C to 95°C
(176°F to 203°F) under normal conditions. The coolant circuit includes a
thermostatic bypass that facilitates rapid warm-up and reduces internal friction
during cold starts. The cylinder block features optimized coolant passages
directing flow preferentially to the cylinder head and the exhaust valve bridge
areas.
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 variable geometry turbocharger from approximately 170°C (338°F) to 50°C
(122°F) before it enters the intake manifold. This cooling of the intake charge
increases air density and combustion efficiency. A viscous fan clutch drives the
engine cooling fan, engaging based on coolant temperature, charge air
temperature, and transmission oil temperature. The total coolant capacity for
the engine and cooling system is approximately 28 liters (7.4 US gal).
Air Intake and Turbocharging: The 6M70 is equipped with
a variable geometry turbocharger (VGT) on later variants and high-output
applications. The VGT system adjusts the angle of the turbine vanes to optimize
boost pressure across the engine speed range, providing responsive low-end
torque while maintaining efficiency at high engine speeds. The intake system
includes a mass air flow sensor, intake air temperature sensor, and a throttle
valve used primarily for exhaust gas recirculation control.
Engine Management: The engine utilizes a Mitsubishi electronic control unit that
monitors crankshaft position, camshaft position, boost pressure, intake air
temperature, coolant temperature, fuel rail pressure, and exhaust gas oxygen
content. It controls injection timing, injection quantity, variable geometry
turbocharger vane position, and the exhaust gas recirculation valve position.
The system is integrated with the vehicle’s transmission control unit for
optimized shift scheduling.
Exhaust System: To comply with emissions regulations, the exhaust system
incorporates a cooled exhaust gas recirculation (EGR) system with an EGR cooler
that reduces the temperature of recirculated exhaust gas, lowering combustion
temperatures and reducing NOx formation. Depending on the market and emissions
standard, a diesel oxidation catalyst (DOC), diesel particulate filter (DPF),
and selective catalytic reduction (SCR) system with AdBlue injection are present
in the exhaust tract. The exhaust manifold is constructed from high-alloy cast
iron and is designed for durability under thermal cycling.
The engine length, measured from the front gear train
housing to the flywheel housing face, is 1,450 mm (57.1 in). The width is 950 mm
(37.4 in) at the widest point, which includes the injection pump, fuel filter,
and exhaust manifold. The height, measured from the oil pan bottom to the top of
the cylinder head cover, is 1,150 mm (45.3 in).
The dry weight (without fluids, starter, alternator, or clutch or transmission)
is 750 kg (1,653 lb). The fully dressed weight for a truck application,
including the alternator, starter, air compressor, power steering pump, and
fluids, is 850 kg (1,874 lb).
The service life of the 6M70 under proper operating
conditions is engineered to exceed 800,000 km (497,000 mi) in on-highway
applications, with many units reaching 1,000,000 km (621,000 mi) before major
overhaul. Oil change intervals are determined by the engine management system
based on fuel consumption, operating hours, and load profiles, with a maximum
interval of 40,000 km (25,000 mi) or 800 operating hours under favorable
conditions. The engine requires a low-ash, synthetic 10W-40 or 15W-40 engine oil
meeting Mitsubishi Fuso specification.
Valve clearance is automatically maintained by hydraulic lash adjusters and
requires no periodic adjustment. Replacement of the fuel filter is mandated
every 40,000 km (25,000 mi) or 24 months. The air cleaner element requires
replacement every 40,000 km (25,000 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 100,000 km (62,000 mi) or sooner if cracking or wear is evident.
The cylinder head bolts follow a multi-stage angular
torque procedure. For the M16 cylinder head bolts, the initial torque is 175 Nm
(129 lb-ft), followed by a 90-degree to 105-degree angle in a specified
sequence. The main bearing cap bolts are torqued to 115 Nm (85 lb-ft) plus a
60-degree angle. The connecting rod bolts are tightened to 115 Nm (85 lb-ft)
with no additional angular turn required.
The rocker arm shaft pedestal bolts are torqued to 50 Nm (37 lb-ft). The
flywheel-to-crankshaft bolts receive a torque of 250 Nm (184 lb-ft) plus a
90-degree angle. The camshaft bearing cap bolts are torqued to 55 Nm (41 lb-ft).
The injector hold-down bolts require 30 Nm (22 lb-ft) plus a 60-degree angle.
The front gear train cover bolts are torqued to 25 Nm (18 lb-ft).
The 6M70 served as the primary heavy-duty diesel engine
for the Mitsubishi Fuso Super Great truck series across multiple generations. In
this application, the engine was offered in various power ratings to suit
different gross vehicle weight classes, from regional distribution
configurations to heavy-haulage tractor units. The engine was also installed in
Mitsubishi Fuso heavy-duty bus chassis, including the Aero Queen and Aero Star
series, where its low noise and vibration characteristics were valued for
passenger comfort.
Beyond Fuso-branded vehicles, the 6M70 found application in Mitsubishi-branded
heavy commercial vehicles for export markets, particularly in Southeast Asia,
the Middle East, Africa, and South America. The engine was utilized in
specialized applications including concrete mixer trucks, dump trucks, and
refuse collection vehicles where low-end torque and durability are critical.
Industrial derivatives of the 6M70 were produced for stationary power
generation, irrigation pumps, and construction equipment such as wheel loaders
and excavators requiring compact, high-torque diesel power units. The engine
remains in production for certain markets and continues to be supported through
Mitsubishi Fuso’s global service network.
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