Mitsubishi 6D40 Specifications
| Engine Model: Mitsubishi 6D40 |
| Engine Type: 4-cycle inline 6-cylinder liquid-cooled diesel |
| Total Displacement: 733.7 cu.in (12.02 L) |
| Rated Engine Power: 330-390 Hp (243-287 kW) at 2200 rpm |
| Fuel System Type: Direct injection |
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The Mitsubishi 6D40 is a 12.0-liter, 24-valve,
inline 6-cylinder diesel engine that served as a flagship power unit for
Mitsubishi Fuso's heavy-duty Super Great trucks and large highway buses,
including the Aero Queen, during the 1990s. Introduced in 1989 to meet
stringent Japanese exhaust emission regulations, the 6D40 was engineered
as a turbocharged and intercooled powerplant for high-speed
transportation, delivering an excellent balance of fuel economy and
drivability. The basic structure of the 6D40 was designed with high
rigidity to permit elevated cylinder pressures.
Advanced engineering features for its era included a 4-valve cylinder
head design, roller cam followers with needle roller bearings, shortened
exhaust ports to reduce friction and heat losses, and pistons with
integrated cooling channels. The Mitsubishi 6D40 utilized a
prestroke-controlled electronic fuel injection pump for flexible and
precise control over injection rate and timing. This engine was produced
in multiple power variants, ranging from 330 to 390 Hp, and powered the
Fuso Super Great chassis codes 410, 410S, and 410L throughout its
production run from 1989 to 1996.
The Mitsubishi 6D40 is an inline, 4-cycle, water-cooled, turbocharged
and intercooled diesel engine. The engine features six cylinders
arranged in a straight configuration. Total displacement measures 12,023
cubic centimeters, equivalent to 12.0 liters or 733.7 cubic inches. The
bore is 135 mm (5.31 in) with a stroke of 140 mm (5.51 in), producing an
undersquare design that prioritizes torque production at lower engine
speeds. The compression ratio is approximately 17.5:1. The firing order
is 1-5-3-6-2-4, standard for inline six-cylinder engines to achieve
primary and secondary balance.
The engine management system employs an electronically controlled fuel
injection pump (prestroke-controlled) capable of flexible and precise
control of both fuel injection rate and timing. Aspiration is provided
by a turbocharger with an intercooler (air-to-air or air-to-water) for
all standard road variants. Power output varies by the specific T-code
designation found in the vehicle model code. The 6D40T1 produces 350 Hp
(258 kW) and meets 1989 Japanese exhaust emission regulations.
The 6D40T2 is rated at 330 Hp (243 kW), while the 6D40T3 produces 390 Hp
(287 kW) at 2,200 rpm. Maximum torque is approximately 1,470 to 1,570 Nm
(1,084 to 1,158 lb-ft) achieved at 1,200 rpm. Engine idling speed is set
between 500 and 600 rpm. The brake-specific fuel consumption (BSFC)
reaches an optimal level of 189 g/kWh at 1,600 rpm, demonstrating the
engine's thermal efficiency.
The cylinder block is constructed from high-tensile cast iron with a
deep-skirt design for maximum rigidity. The 6D40 uses replaceable wet
cylinder liners that are pressed into the block. These liners are
centrifugally cast from a high-alloy iron featuring a plateau-honed
internal surface to reduce oil consumption and ring wear. The block
incorporates seven main bearing bulkheads supporting a forged steel
crankshaft with induction-hardened journal surfaces. The crankshaft is
supported by seven main bearings, a configuration that provides
exceptional rigidity for sustained high-load operation.
The block was designed using a CAD system and assessed beforehand by
finite element method (FEM) analyses to optimize force distribution
without unnecessary weight. Piston cooling jets (oil squirters) are
installed in the block directly below each cylinder, directing a
continuous stream of engine oil to the underside of each piston crown to
dissipate heat generated during high-load operation. The oil pan is a
fabricated steel design with a large sump capacity suitable for extended
service intervals.
The cylinder head is a single cast iron unit covering all six cylinders.
The valvetrain is an overhead camshaft (OHC) design with four valves per
cylinder, yielding a total of 24 valves. Each cylinder has two intake
valves and two exhaust valves. The 4-valve configuration maximizes
airflow and improves volumetric efficiency across the operating range.
The camshaft is located high in the cylinder head to shorten the valve
train. Roller cam followers with needle roller bearings are adopted to
reduce friction and heat losses. The camshaft is driven by a gear train
at the front of the engine, eliminating belts or chains.
The combustion chamber is of the direct injection type with a
bowl-in-piston design. The intake ports have been shortened to reduce
flow resistance, while the exhaust ports are designed to maintain
exhaust gas energy for the turbocharger. The cylinder head gasket is a
laminated-steel type (multi-layer steel) capable of sealing high
combustion pressures generated by the electronic injection system. Valve
clearance adjustment is performed manually with the engine cold. Intake
valve clearance (cold) is 0.40 mm (0.016 in). Exhaust valve clearance
(cold) is 0.60 mm (0.024 in).
The fuel system is a direct injection diesel system employing an
electronically controlled in-line injection pump. Mitsubishi's original
prestroke-controlled fuel injection pump was adopted for the 6D40,
capable of flexible and precise control of both fuel injection rate and
timing. A gear-type supply pump draws fuel from the tank and delivers it
to the high-pressure injection pump. The injection pump is driven by the
engine's gear train. The electronic control system adjusts injection
timing and fuel quantity based on engine speed, load, boost pressure,
and coolant temperature.
Early versions of the 6D40 used a mechanical pump with an electronic
governor (RED-III system), while later variants incorporated more
advanced electronic controls. The injection nozzles are of the
multi-hole type designed for direct injection combustion. A
hand-operated primer pump is located on the fuel filter housing to bleed
air from the system. The fuel filter is a spin-on type with water
separation capability. The system operates with diesel fuel meeting a
minimum cetane number of 45 for reliable cold starting.
The lubrication system is a full-pressure design using a gear-type oil
pump driven directly from the crankshaft nose. The pump draws oil from
the sump through a screened pickup tube and forces it through a
full-flow spin-on oil filter mounted on the side of the block. The
filtered oil then passes through a shell-and-tube type oil cooler
integrated into the coolant circuit. From the cooler, oil circulates
through a main gallery drilled longitudinally through the cylinder
block. Cross-drilled passages supply the seven main bearings, connecting
rod bearings, and camshaft bearings.
A separate gallery supplies the piston cooling jets, which continuously
spray oil against the underside of each piston crown. The oil capacity
varies with the oil pan configuration but ranges from 31 to 36 liters
(32.8 to 38.0 quarts), including the filter and cooler. Operating oil
pressure at rated speed (2,200 rpm) with the oil at operating
temperature is 350 to 450 kPa (51 to 65 psi). A pressure relief valve
located at the oil pump outlet prevents over-pressurization during cold
starts. Recommended oil viscosity is 15W-40 meeting API CI-4 or higher
specification.
The cooling system is a pressurized, thermostatically controlled design
with a belt-driven centrifugal water pump mounted at the front of the
engine. Coolant circulates from the radiator bottom tank through the
water pump, then enters the cylinder block at the front and flows
rearward through the water jacket surrounding the wet cylinder liners. A
water distribution duct cast into the cylinder block side ensures even
coolant flow to each cylinder liner.
Coolant rises through ports in the cylinder head gasket into the
cylinder head, where it flows around the exhaust valve seats, injector
nozzles, and the camshaft area before exiting through the thermostat
housing at the front of the head. A wax-pellet thermostat with a nominal
opening temperature of 82 to 88°C (180 to 190°F) controls coolant flow
to the radiator.
A bypass circuit allows coolant to circulate within the engine without
passing through the radiator until operating temperature is achieved. A
radiator with an engine-driven fan provides heat rejection. A radiator
pressure cap rated at 50 to 80 kPa (7 to 12 psi) maintains system
pressure, raising the boiling point of the coolant. The cooling system
requires a 40 to 50 percent mixture of ethylene glycol antifreeze with
distilled water.
| Intake and Exhaust Systems |
Intake System: A dry-type replaceable paper air filter element with a
restriction indicator is mounted remotely from the engine. The filtered
air passes through a rubber hose to the turbocharger inlet. A silencer
integrated into the air intake system reduces induction noise.
Exhaust System: A cast iron exhaust manifold with divided passages
delivers exhaust pulses efficiently to the turbocharger turbine inlet.
The exhaust outlet is a standard flange for connection to the vehicle
exhaust piping. Some variants were equipped with an exhaust brake
(mountain brake) for additional retardation on downhill grades.
Turbocharging and Intercooling System: The 6D40 is equipped with a
turbocharger mounted to a cast iron exhaust manifold. The turbocharger
uses exhaust gas energy to drive a compressor wheel, increasing intake
air density. Compressed air then passes through an intercooler
(charge-air cooler) mounted in front of the radiator. The intercooler
reduces intake air temperature to within 10 to 15°C (18 to 27°F) of
ambient before the air enters the intake manifold. Lower intake air
temperature increases charge density and reduces exhaust gas
temperature, improving fuel efficiency and reducing NOx formation.
Electrical System: 24-volt system with a negative ground (standard for
heavy-duty trucks). The starter motor is a reduction-gear type rated at
5.5 to 7.5 kW. The alternator is rated at 35 to 50 amperes depending on
vehicle equipment. Glow plugs are fitted for cold starting assistance in
low ambient temperatures.
Timing System: The camshaft and fuel injection pump are driven by a gear
train at the front of the engine. A gear on the crankshaft drives an
idler gear, which in turn drives the camshaft gear and the injection
pump gear. This all-gear system requires no periodic replacement.
Overall length, measured from the front timing gear cover to the
flywheel housing mating surface, is 1,420 mm (55.9 in). Overall width,
measured across the widest point including the turbocharger and
injection pump, is 830 mm (32.7 in). Overall height, measured from the
bottom of the oil pan to the top of the cylinder head, is 1,080 mm (42.5
in).
The dry weight of the complete engine, inclusive of the turbocharger,
intercooler, injection pump, alternator, starter motor, and flywheel
housing, is 1,080 kg (2,380 lb). The long block assembly (cylinder
block, crankshaft, connecting rods, pistons, and cylinder head) weighs
850 kg (1,874 lb). The forged steel crankshaft with seven main bearing
journals contributes 180 kg (397 lb).
Regular maintenance intervals for the 6D40 are dictated by operating
hours or distance traveled, depending on the application. The engine oil
and filter change interval is 500 hours for industrial applications or
20,000 km (12,500 miles) for on-highway truck use. Oil capacity with
filter change ranges from 31 to 36 liters (32.8 to 38.0 quarts)
depending on oil pan depth. Recommended oil viscosity is 15W-40 meeting
API CI-4 or CJ-4 specifications.
The fuel filter requires replacement every 500 hours or 20,000 km
(12,500 miles). The water separator must be drained weekly or whenever
the water-in-fuel warning lamp illuminates. The air cleaner element
requires replacement when the restriction indicator shows excessive
vacuum, or at a maximum interval of 1,000 hours under normal conditions.
The engine coolant requires replacement every 2,000 hours or 24 months.
Valve clearance inspection and adjustment is required every 1,500 hours
or 60,000 km (37,500 miles). Intake valve clearance (cold) is 0.40 mm
(0.016 in). Exhaust valve clearance (cold) is 0.60 mm (0.024 in). The
drive belts (alternator, water pump, power steering) require inspection
at every oil change for cracking or glazing, with replacement at 1,000
hours. A compression test is recommended if hard starting or excessive
blow-by is observed.
Standard compression pressure is 2.55 MPa (370 psi) at 200 rpm. The
minimum acceptable compression pressure is 1.96 MPa (284 psi) at the
same cranking speed. The maximum allowable variation in compression
pressure between any two cylinders is 0.29 MPa (42 psi). The injection
pump timing is set at the factory and does not require routine
adjustment unless the pump is removed. The turbocharger should be
inspected for oil leakage and shaft play every 1,000 hours.
Cylinder Head Bolts: 175 Nm (129 lb-ft.
Connecting Rod Bolts: 115 Nm (85 lb-ft).
Main Bearing Cap Bolts: 115 Nm (85 lb-ft).
Crankshaft Pulley Bolt (Center Bolt): 450 Nm (332 lb-ft).
Flywheel Bolts (to Crankshaft Flange): 315 Nm (232 lb-ft).
Camshaft Bearing Cap Bolts: 25 Nm (18 lb-ft).
Rocker Arm Shaft Bracket Bolts: 40 Nm (30 lb-ft).
Intake Manifold Bolts: 45 Nm (33 lb-ft).
Exhaust Manifold Nuts: 55 Nm (41 lb-ft).
Turbocharger Mounting Nuts (to Exhaust Manifold): 50 Nm (37 lb-ft).
Turbocharger Oil Supply Line Fitting: 30 Nm (22 lb-ft).
Injector Hold-Down Bolts: 70 Nm (52 lb-ft).
Glow Plugs: 15 Nm (11 lb-ft).
Water Pump Mounting Bolts: 25 Nm (18 lb-ft).
Oil Pan Bolts (M10): 35 Nm (26 lb-ft).
Oil Pan Drain Plug: 70 Nm (52 lb-ft).
Timing Gear Cover Bolts (M8): 25 Nm (18 lb-ft).
Front Engine Mount Bracket Bolts (to Block): 120 Nm (89 lb-ft).
Flywheel Housing to Block Bolts: 180 Nm (133 lb-ft).
Starter Motor Mounting Bolts: 80 Nm (59 lb-ft).
Alternator Mounting Bolts: 45 Nm (33 lb-ft).
Injection Pump Drive Gear Nut: 150 Nm (111 lb-ft).
The Mitsubishi 6D40 engine was deployed across a range of heavy-duty
trucks and buses produced by Mitsubishi Fuso during the 1990s.
Mitsubishi Fuso Super Great (Chassis Code 410, 410S, 410L, 1989-1996):
The primary application for the 6D40 engine in heavy-duty truck
configurations. The 6D40T1 (350 PS), 6D40T2 (330 PS), and 6D40T3 (390
PS) were offered across various GVW ratings.
Mitsubishi Fuso The Great (Heavy-Duty Truck Series): The predecessor to
the Super Great, receiving the 6D40 in later production years.
Mitsubishi Fuso Aero Queen (Highway Bus): Used in high-deck touring bus
applications requiring sustained high-speed operation and low emissions.
Mitsubishi Fuso Aero Ace (Highway Bus): An additional bus platform
utilizing the 6D40 for intercity and touring service.
Mitsubishi Fuso Fighter (Heavy-Duty Variants): Select heavy-duty
configurations of the Fighter medium-duty truck range received the 6D40
as an optional power unit.
Industrial Power Units: Stationary versions of the 6D40 were supplied
for generator sets, irrigation pumps, and industrial machinery, often
with modified governor settings for constant-speed operation.
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