Mitsubishi 6D20 Specifications
| Engine Model: Mitsubishi 6D20 |
| Engine Type: 4-cycle inline 6-cylinder liquid-cooled diesel |
| Total Displacement: 629 cu.in (10.3 L) |
| Rated Engine Power: 212 Hp (158 kW) at 2500 rpm |
| Fuel System Type: Direct injection |
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The Mitsubishi 6D20 is a 10.3-liter, naturally
aspirated inline-six diesel engine produced by Mitsubishi Motors, later
Mitsubishi Fuso Truck and Bus Corporation. Introduced in 1975 with
production commencing in 1976, this engine served as a heavy-duty
powerplant for large commercial vehicles, including the Mitsubishi Fuso
F-series trucks, as well as industrial equipment such as forklifts,
rough terrain cranes, and construction machinery. The 6D20 belongs to
the broader 6D2 engine family, which also includes the larger 6D21 and
the later 4-valve 6D40 variants.
The engine features a cast iron cylinder block with direct injection
combustion and an overhead valve valvetrain with two valves per
cylinder. The square bore and stroke dimensions - both 130 mm -
contribute to a favorable torque curve for heavy commercial use. The
Mitsubishi 6D20 earned a reputation for exceptional durability,
straightforward serviceability, and high torque output at low engine
speeds, making it suitable for continuous operation in demanding
environments. Production continued through the late 1970s, with later
variants appearing in early 1980s applications before being succeeded by
more advanced engine families.
Engine Type: Inline-6, four-stroke, water-cooled, diesel.
Displacement: 10,308 cc (10.3 L / 629 cu.in).
Bore and Stroke: 125 mm x 140 mm (4.92 in x 5.51 in).
Compression Ratio: 17.0:1.
Combustion System: Direct injection.
Valvetrain: OHV, 2 valves per cylinder, pushrod-actuated.
Firing Order: 1-5-3-6-2-4.
Maximum Power: 215 PS (158 kW / 212 hp) at 2,500 rpm.
Maximum Torque: 70.0 kgm (686 Nm / 506 lb-ft) at 1,600 rpm.
Rated Speed: 2,500 rpm.
Compression Pressure (Standard): 28 kg/cm2 (2.75 MPa / 398 psi).
Compression Pressure (Minimum): 20 kg/cm2 (1.96 MPa / 284 psi).
The cylinder block is constructed from high-strength cast iron, a
material selection providing the rigidity and vibration damping required
for sustained heavy-duty diesel operation. This robust construction is
essential for the engine's ability to withstand high cylinder pressures
and thermal loads inherent to direct injection diesel combustion. The
block incorporates seven main bearing bulkheads, a configuration that
provides full crankshaft support across the six cylinder throws. The
deep-skirt design extends the block below the crankshaft centerline,
enhancing structural rigidity and minimizing torsional flex under load.
The block design includes replaceable wet-type cylinder liners, a
significant advantage for commercial vehicle operators. This feature
permits complete engine overhaul without removing the engine from the
chassis, as the liners can be extracted and replaced while the block
remains installed in the vehicle frame.
The block includes cast water jacket passages surrounding each cylinder
liner for uniform coolant distribution and thermal management. An
integral oil sump mounting flange with a gasket sealing surface provides
attachment for the pressed steel oil pan. The block also features an
integral timing gear housing at the front for driving the camshaft,
injection pump, and auxiliary components.
The cylinder head is a single-piece cast iron unit that houses the
direct injection combustion chambers. Cast iron construction is
specified for this diesel application to provide the thermal mass and
durability required for sustained high-load operation. The head
incorporates individual pre-combustion chambers positioned centrally
above each piston, a design that promotes thorough air-fuel mixing and
complete combustion. The valve arrangement follows a parallel or
slightly inclined layout, maintaining simplicity in the valvetrain.
The valvetrain operates on an overhead valve (OHV) configuration with
pushrods and rocker arms. The camshaft is located within the cylinder
block and driven by a gear train at the front of the engine. Each
cylinder receives two valves: one intake and one exhaust. The valves are
arranged in a single row along the cylinder head centerline. Hardened
valve seat inserts are pressed into the cylinder head and machined to
precise angles for positive sealing against diesel combustion pressures.
The valve guides are pressed into the head and sized to the valve stems.
The rocker arm assembly is supported on a single shaft running the
length of the cylinder head. Individual screw-type adjusters with
locking nuts provide precise valve lash adjustment. The valve cover is a
stamped steel component sealed by a reusable gasket.
The fuel system employs a mechanical direct injection design. The
injection pump is a Bosch in-line type pump, model PES or M-series,
mounted on the side of the cylinder block and driven by a gear from the
camshaft or timing gear train. The in-line pump configuration features
individual plunger and barrel assemblies for each cylinder, each
delivering fuel at a pressure calibrated to the injector opening
requirements. The pump incorporates a mechanical governor that maintains
engine speed under varying loads, a critical feature for commercial
vehicle applications where consistent power delivery is required.
High-pressure injection lines carry fuel from the in-line pump to
individual injectors mounted in the cylinder head. The injectors are of
the nozzle-and-holder type, calibrated to open at a specific injection
pressure. The direct injection system delivers fuel directly into the
combustion chamber formed in the piston crown. A fuel filter with an
integrated water separator is mounted between the fuel tank and the
injection pump. This component is essential for diesel systems, as water
contamination from fuel storage can cause corrosion and premature wear
of the precision injection pump components.
The lubrication system is a fully pressurized, wet-sump design with a
gear-type oil pump mounted inside the oil pan or on the front of the
engine block. The pump draws oil through a screened pickup tube
positioned at the lowest point of the oil pan to maintain suction even
when the vehicle operates on inclines. The pump delivers oil to a
full-flow spin-on oil filter mounted on the cylinder block. The
full-flow configuration ensures that all oil circulated by the pump
passes through the filter before reaching bearing surfaces, removing
contaminants during every pass.
From the filter, oil circulates through main oil galleries drilled
longitudinally through the block, supplying the crankshaft main
bearings, connecting rod bearings, camshaft bearings, and the rocker arm
assembly through external oil feed tubes. An oil pressure relief valve,
integrated into the pump housing, opens at a calibrated pressure to
prevent over-pressurization during cold starts. Normal operating oil
pressure ranges from 35-55 psi (241-379 kPa) at rated speed. Oil
capacity with filter change is substantial, reflecting the engine's
large displacement and commercial application.
The cooling system is a pressurized, thermostatically controlled liquid
cooling setup with a belt-driven centrifugal water pump. Coolant
circulates from the radiator lower tank through the water pump, into the
cylinder block water jacket, upward through the cylinder head, and
returns to the radiator upper tank. The system incorporates a wax-type
thermostat with a nominal opening temperature that maintains engine
operating temperature within the designed range, allowing the engine to
reach optimal thermal efficiency quickly while preventing overheating
under sustained load.
A belt-driven fan, mounted on the water pump hub and enclosed in a fan
shroud, draws air through the radiator core. The cooling system is
pressurized by a radiator cap with a pressure relief valve, raising the
boiling point of the coolant for operation under load. Coolant capacity
for the engine block and cylinder head is substantial, with the radiator
adding additional volume depending on the specific vehicle application.
| Intake and Exhaust Systems |
Air Intake System: A dry-type air cleaner with a replaceable paper
filter element is mounted on the intake side of the engine. Heavy-duty
applications in dusty environments use a dual-element air cleaner with a
primary filter and a secondary safety filter to protect the engine.
Exhaust System: The engine includes an exhaust manifold on the left side
of the cylinder head, directing combustion gases to the exhaust pipe.
Later applications include an oxidation catalyst for Euro III emissions
compliance.
Electrical System: The engine uses a 12-volt or 24-volt electrical
system depending on the vehicle application. Heavy commercial trucks and
construction equipment often specify 24-volt systems for improved cold
starting and reduced current draw in long wiring runs. A belt-driven
alternator supplies charging current to the battery or batteries.
Starting System: A high-torque starter motor engages the flywheel ring
gear for engine cranking. Cold starting assistance is provided by glow
plugs or an intake air heater, depending on the emissions configuration
and market requirements.
Timing System: The camshaft and injection pump are driven by a gear
train at the front of the engine. The gear train provides precise timing
without the maintenance or replacement concerns associated with belt or
chain drives, contributing to the engine's reputation for reliability in
commercial service.
Governor System: The mechanical governor is integrated into the
injection pump housing. A flyweight mechanism senses engine speed and
adjusts the fuel control rack position to maintain the selected engine
speed regardless of load variations.
Overall length from the front timing gear cover to the flywheel housing
mounting face is 1,500 mm (59 in). Width, measured across the cylinder
head and injection pump, is 800 mm (31 in). Height from the oil pan rail
to the top of the valve cover is 1,100 mm (43 in). The complete engine
dry weight is 900 kg (1,984 lb). The cast iron cylinder block, cylinder
head, and large rotating components contribute the majority of this
mass.
Engine Oil Capacity: With filter change, 20-25 L (21-26 US qt),
depending on the specific oil pan configuration and vehicle application.
Recommended Oil Viscosity: 15W-40 for diesel service. API
Classification: CD, CE, or CF for diesel service. The engine predates
electronic control units, making it compatible with mineral-based diesel
oils. Oil Change Interval: 5,000-10,000 km (3,100-6,200 miles) under
normal conditions, more frequent under severe service.
Coolant Capacity: Engine and radiator combined, approximately 18-25 L
(19-26 US qt) depending on the vehicle application. Coolant Type:
Ethylene glycol antifreeze for diesel engines with supplemental coolant
additives (SCAs) for wet liner protection. Water Pump Inspection: Known
weak point requiring attention after 250,000 km (155,000 miles) due to
impeller erosion. Coolant pH Monitoring: Required at regular intervals
to prevent corrosion of wet cylinder liners.
Valve Clearance Adjustment (Cold Engine): Intake: 0.40 mm (0.016 in).
Exhaust: 0.60 mm (0.024 in). Valve Clearance Adjustment Interval: Every
40,000 km (25,000 miles). Compression Pressure (Standard): 28 kg/cm2
(398 psi). Compression Pressure (Service Limit): 20 kg/cm2 (284 psi).
Injection Pump Timing: Consult the specific engine manual for the
correct timing setting, expressed in degrees before top dead center.
Idle Speed: 600-700 rpm in neutral. Fuel Filter Replacement Interval:
5,000-10,000 km or 250-500 operating hours. Air Filter Replacement
Interval: As indicated by restriction indicator or every 10,000-20,000
km (6,200-12,400 miles) in normal conditions. Injector Inspection
Interval: Every 1,000 operating hours.
Cylinder Head Bolts: 132 lb-ft (180 Nm).
Connecting Rod Cap Nuts: 90-100 lb-ft (122-136 Nm).
Main Bearing Cap Bolts: 150-180 lb-ft (203-244 Nm).
Flywheel Bolts: 80-90 lb-ft (108-122 Nm).
Crankshaft Pulley Bolt: 250-300 lb-ft (339-407 Nm).
Rocker Arm Shaft Bracket Bolts: 25-30 lb-ft (34-41 Nm).
Camshaft Thrust Plate Bolts: 18-22 lb-ft (24-30 Nm).
Intake Manifold Nuts: 25-30 lb-ft (34-41 Nm).
Exhaust Manifold Nuts: 25-30 lb-ft (34-41 Nm).
Injector Hold-Down Clamp Bolts: 18-22 lb-ft (24-30 Nm).
Injection Pump Mounting Nuts: 20-25 lb-ft (27-34 Nm).
Oil Pan Bolts: 12-15 lb-ft (16-20 Nm).
Valve Cover Bolts: 6-8 lb-ft (8-11 Nm).
Water Pump Mounting Bolts: 25-30 lb-ft (34-41 Nm).
Starter Motor Mounting Bolts: 35-40 lb-ft (47-54 Nm).
Alternator Mounting Bolts: 35-40 lb-ft (47-54 Nm).
Engine Mounting Bolts: 60-70 lb-ft (81-95 Nm).
The Mitsubishi 6D20 engine was installed in heavy commercial vehicles,
construction equipment, and industrial machinery from 1976 through the
early 1980s.
Mitsubishi Fuso F-Series (FP/FT Models): The primary application of the
6D20 engine. Installed in large trucks from 1976 to 1979. These trucks
served in long-haul freight and heavy distribution roles.
Mitsubishi Fuso MP117 and MP517 Bus Chassis: These passenger bus
applications used the 6D20 engine for public transport and touring
coaches.
Mitsubishi The Great / Super Great (KC-FU/FT/FN/FS): The successor to
the F-series, these large trucks continued to use the 6D20 engine in
early production variants.
Mitsubishi Fuso KC-MP217/237/617/637: Heavy bus chassis applications.
Mitsubishi Fuso KC-MP317/337/717/737/747: Additional bus chassis
configurations.
NICHIYU Mitsubishi Forklift FD380 and FD420: Industrial forklift
applications using the 6D20 engine.
NICHIYU Mitsubishi Reach Stacker RS450: Material handling equipment.
Hyundai Commercial Vehicles: Hyundai Motor Company directly imported
Mitsubishi vehicles and fitted the 6D20 engine to 8.5-ton special
vehicles, including 10,000-liter tank lorries, in the late 1970s and
early 1980s.
Construction and Industrial Equipment: The 6D20 powered excavators,
loaders, bulldozers, and rough terrain cranes. These applications
demanded high torque at low engine speeds for continuous operation.
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