Mitsubishi 8DC8 Specifications
| Engine Model: Mitsubishi 8DC8 |
| Engine Type: 4-cycle 8-cylinder V-block naturally aspirated liquid-cooled diesel |
| Total Displacement: 908.4 cu.in (14.88 L) |
| Rated Engine Power: 275-305 Hp (202-225 kW) at 2200 rpm |
| Fuel System Type: Direct injection |
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The Mitsubishi 8DC8 is a heavy-duty, naturally
aspirated V8 diesel engine produced by Mitsubishi Motors Corporation and
later by Mitsubishi Fuso Truck and Bus Corporation. Introduced in the
mid-1970s, this engine belongs to the DC series and represents a
significant evolution from earlier indirect injection designs. The 8DC8
features direct injection, a departure from the pre-combustion chamber
configuration found in the preceding 8DC6 series.
Engineers designed this 14.88-liter powerplant for the Mitsubishi Fuso
"The Great" truck series, heavy industrial machinery including cranes,
large generators, and intercity coaches such as the Mitsubishi Fuso Aero
Bus. The 8DC8 produces power outputs ranging from 275 to 305 hp
depending on the emissions regulation year and specific application. A
90-degree V8 architecture provides a compact overall length relative to
its displacement, enabling installation in cab-over truck designs.
The engine operates on a 24V electrical starting system with a
high-output starter motor. Known for durability and high torque at low
engine speeds, the 8DC8 remained in production through the mid-1990s,
receiving updates to meet Japan's 1983, 1986, and 1989 emissions
regulations. Hyundai Motor Company produced this engine under license in
South Korea, installing it in the Hyundai 91A truck and Aero Bus models.
The Mitsubishi 8DC8 is a four-stroke, water-cooled, 90-degree V8 diesel
engine. Total displacement measures 14.88 liters (14,886 cc), equivalent
to 908.4 cubic inches. Bore is 135 mm (5.31 in) with a stroke of 130 mm
(5.12 in). The compression ratio is 17.5:1. The combustion system uses
direct injection, with fuel injected directly into the piston bowl.
Aspiration is naturally aspirated without turbocharging or aftercooling.
Power output varies by emissions regulation year. The 1979-1991 versions
produce 305 hp (225 kW) at 2300 rpm.
The 1992-1996 version, meeting Japan 1992 emissions regulations,
produces 275 hp (202 kW) at 2300 rpm. Mid-production versions for Japan
1986 regulations produce 290 hp (213 kW). Peak torque is approximately
980 Nm (723 lb-ft) achieved at 1400 rpm. The firing order is
1-8-4-2-7-3-6-5. Dry weight of the complete engine is approximately 850
kg (1874 lb). The electrical system operates at 24V. Cold valve
clearance is 0.50 mm (0.020 in) for intake valves and 0.60 mm (0.024 in)
for exhaust valves.
The cylinder block is constructed from high-strength cast iron with a
90-degree V configuration. Two separate cylinder banks, each containing
four cylinders, are cast as a single integrated unit at a 90-degree
included angle. The block incorporates five main bearing webs, each
cross-bolted for additional rigidity under high cylinder pressures. A
deep-skirt design extends the block below the crankshaft centerline,
providing enhanced torsional stiffness and vibration damping.
The cylinder block uses dry-type cylinder liners pressed into the parent
casting. Each liner is a centrifugally cast iron tube with a precise
external diameter matching the block bore. Dry liners do not contact
engine coolant directly; heat transfers from the liner through the block
wall to the coolant passages surrounding each cylinder cavity. Each
liner features a flange at the top that seats against a counterbore in
the block deck. Coolant passages surround each cylinder bore within the
block casting.
The block includes a side-mounted camshaft driven by a gear train at the
front. An integral timing gear housing is cast into the front face. The
cylinder block includes mounting pads for the in-line injection pump on
the left bank, the 24V starter motor, the alternator, and the water
pump. Cast internal oil galleries direct pressurized lubricant to all
main bearings, connecting rod bearings, camshaft bearings, and piston
cooling jets.
Two separate cylinder heads are used, one for each cylinder bank. Each
head is cast from gray iron and spans four cylinders in a cross-flow
design. Intake ports are located on the inside of the V (valley side),
exhaust ports on the outside of each bank. The valvetrain operates as an
overhead valve (OHV) configuration with two valves per cylinder - one
intake and one exhaust - for a total of 16 valves across the engine. A
single camshaft located within the cylinder block actuates the
valvetrain.
Pushrods transfer motion from the camshaft to rocker arms mounted on
shafts within each cylinder head. Intake valves are larger in diameter
than exhaust valves. Hardened valve seat inserts are pressed into each
cylinder head, with exhaust seats manufactured from a nickel-chromium
heat-resistant alloy. Valve guides are replaceable cast-iron sleeves.
Valve lash is adjusted using a screw-and-locknut mechanism on each
rocker arm.
Cold intake valve clearance is 0.50 mm (0.020 in). Cold exhaust valve
clearance is 0.60 mm (0.024 in). Each cylinder head uses a steel
laminate gasket. Six head bolts surround each cylinder, with two
different bolt sizes used. M16 bolts require 285 Nm (210 lb-ft). M14
bolts require 175 Nm (129 lb-ft). The direct injection system places the
fuel injector centrally in each cylinder head, angled toward the piston
bowl.
The fuel system uses mechanical direct injection with an in-line
injection pump of Bosch design. A mechanical gear-type lift pump mounted
on the cylinder block draws fuel from the tank through a primary spin-on
filter and water separator. The lift pump supplies fuel at low pressure
to the injection pump. The injection pump is an in-line unit containing
eight plunger and barrel assemblies, one for each cylinder, arranged in
a line.
A mechanical centrifugal governor integrated into the pump regulates
fuel delivery based on engine speed and load. The governor includes both
low-idle and high-speed limiting functions. Injection timing is set
manually and is specified between 13 and 16 degrees before top dead
center (BTDC), depending on the pump calibration. A manual fuel shutoff
lever or an electric shutoff solenoid, operating on 24V, provides engine
stop control.
Eight high-pressure steel injection lines carry fuel from the pump to
the injectors. Each injector is a hole-type nozzle with multiple
orifices. Injectors are installed in the cylinder head and positioned to
spray fuel directly into the piston bowl. A fuel return line routes
excess fuel and injector leakage back to the fuel tank.
The lubrication system is a pressurized, full-flow filtration design
using a gear-type positive displacement pump. The pump is mounted on the
front timing gear cover and driven by the crankshaft gear. Oil is drawn
from the oil pan through a pick-up tube fitted with a coarse mesh
strainer. Total oil capacity ranges from 25 to 28 liters, equivalent to
6.6 to 7.4 U.S. gallons. A spin-on full-flow oil filter is mounted
externally on the block. Some configurations include an additional
bypass oil filter.
A pressure relief valve limits maximum oil pressure. Oil jets direct
lubricant to the underside of each piston crown for cooling. The system
supplies lubricant to the five main bearings, eight connecting rod
bearings, camshaft bearings, rocker arm assemblies, timing gears, and
the injection pump driveshaft. Operating oil pressure at rated speed is
maintained between 345 and 450 kPa (50 and 65 psi). The oil pan is
constructed from stamped steel and includes a drain plug with a magnetic
tip to capture ferrous wear particles.
The cooling system is pressurized and thermostatically controlled, using
a centrifugal water pump driven by a V-belt from the crankshaft pulley.
Total cooling system capacity, including the engine block, cylinder
heads, radiator, and all hoses, is 35 to 40 liters (37 to 42 U.S.
quarts). A wax-pellet thermostat is located in a housing on the front of
the engine. The thermostat begins to open at 82°C (180°F) and reaches
full open at 95°C (203°F).
The water pump circulates coolant through passages cast into the
cylinder block surrounding each cylinder bore and dry liner cavity.
Coolant then flows up into both cylinder heads, circulating around the
valve seats and injector sleeves before exiting through the thermostat
housing. The cooling system uses a down-flow or cross-flow radiator
depending on the vehicle manufacturer's design. A pressure cap rated at
maintains system pressure to raise the coolant boiling point. An
engine-driven fan is mounted on the water pump hub.
| Intake and Exhaust Systems |
Air Intake System: Ambient air passes through a dry-type, two-stage air
cleaner before entering the intake manifold. The intake manifold is a
cast-iron plenum mounted between the two cylinder banks within the V.
The manifold distributes air to both cylinder banks through individual
runners. No turbocharger or aftercooler is present on this naturally
aspirated engine.
Exhaust System: Two separate cast-iron exhaust manifolds are used, one
for each cylinder bank. Each manifold collects gases from four
cylinders. The manifolds are flanged for connection to a single exhaust
pipe.
The electrical system operates at 24V DC. A gear-reduction starter motor
rated at 5.5 kW or 7.0 kW is mounted on the flywheel housing, engaging a
ring gear on the flywheel. A belt-driven 24V alternator produces
charging current with output ratings of 25 to 35 amps. Glow plugs are
installed in each cylinder head as a cold start aid, one per cylinder. A
glow plug controller manages pre-heat duration based on coolant
temperature.
Engine length measured from the front gear cover to the flywheel housing
mounting face is 1250 mm (49.2 in). Width measured across the widest
points, including the exhaust manifolds and injection pump, is 950 mm
(37.4 in). Height measured from the oil pan rail to the top of the
cylinder heads is 900 mm (35.4 in).
Dry weight of the complete engine, including the flywheel, injection
pump, alternator, starter motor, and both exhaust manifolds, but
excluding oil and coolant, is 850 kg (1874 lb). The weight with a full
oil charge and coolant adds 60 kg (132 lb). The shipping weight on a
pallet with protective packaging is 920 kg (2028 lb).
Engine Oil: Capacity: 25 to 28 l (6.6 to 7.4 U.S. gal). Oil change
interval: 250 hours or 10,000 km (6,200 miles). Recommended grade: SAE
15W-40 or SAE 20W-50. Oil Filter: Spin-on full-flow type. Replace at
every oil change. Coolant: System capacity: 35 to 40 l (37 to 42 U.S.
qt). Change interval: 2000 hours or 2 years. Fuel Filter: Primary
spin-on with water separator. Replacement interval: 500 hours. Secondary
Fuel Filter: Replace at 500 hours.
Valve Lash (Cold): Intake: 0.50 mm (0.020 in). Exhaust: 0.60 mm (0.024
in). Inspection interval: 500 hours or 20,000 km (12,400 miles). Valve
Lash (Hot): Intake: 0.55 mm (0.022 in). Exhaust: 0.65 mm (0.026 in). Air
Cleaner: Dry cartridge type. Service when restriction indicator shows 5
kPa. Thermostat: Begins opening at 82°C (180°F). Fully open at 95°C
(203°F). Low Idle Speed: 550 to 600 rpm. High Idle Speed (No Load): 2450
rpm maximum.
Fuel Injection Timing: 13 to 16 degrees BTDC. Check every 1500 hours.
Injector Opening Pressure: Check every 1500 hours. Adjust or replace as
needed. Glow Plugs: Resistance check at 500 hours. Battery System: 24V
with two 12V batteries in series. Minimum CCA per battery: 800 at -18°C
(0°F).
Cylinder Head Bolts M16 x 2.0: 285 Nm (210 lb-ft).
Cylinder Head Bolts M14 x 1.5: 175 Nm (129 lb-ft).
Connecting Rod Cap Nuts M12 x 1.25: 225 Nm (166 lb-ft).
Main Bearing Cap Bolts M16 x 2.0: 370 Nm (273 lb-ft).
Flywheel Bolts M12 x 1.25: 315 Nm (232 lb-ft) plus 90 degrees.
Crankshaft Damper Bolt M20 x 1.5: 350 Nm (258 lb-ft) plus 90 degrees.
Camshaft Thrust Plate Bolts: 25 Nm (18 lb-ft).
Rocker Arm Shaft Support Bolts: 35 Nm (26 lb-ft).
Rocker Arm Adjustment Lock Nut: 20 Nm (15 lb-ft).
Valve Cover Nuts: 10 Nm (7 lb-ft).
Injection Pump Mounting Nuts: 25 Nm (18 lb-ft).
Injection Lines (High Pressure): 35 Nm (26 lb-ft).
Injector Hold-Down Bolts: 70 Nm (52 lb-ft).
Glow Plugs: 20 Nm (15 lb-ft).
Oil Pan Drain Plug: 70 Nm (52 lb-ft).
Starter Motor Mounting Bolts (7.0 kW): 70 Nm (52 lb-ft).
Starter Motor Mounting Bolts (5.5 kW): 50 Nm (37 lb-ft).
Alternator Pivot Bolt: 25 Nm (18 lb-ft).
Water Pump Mounting Bolts: 25 Nm (18 lb-ft).
Thermostat Housing Bolts: 20 Nm (15 lb-ft).
Exhaust Manifold Nuts: 40 Nm (30 lb-ft).
Intake Manifold Bolts: 25 Nm (18 lb-ft).
The Mitsubishi 8DC8 engine served across multiple heavy-duty sectors.
Mitsubishi Fuso Trucks: Mitsubishi Fuso The Great series, including
model code 413 vehicles. Mitsubishi FV (heavy-duty) series. Mitsubishi
FU (tractor) series. Mitsubishi FT series. Production years spanned 1983
to 1996 for most applications, with specific installations continuing
through 1998.
Buses: Mitsubishi Fuso Aero Bus intercity coaches. Mitsubishi Fuso Aero
Queen coaches. Industrial Equipment: Large crawler cranes. Tower cranes.
Stationary generator sets rated at 200 kW to 250 kW. Hyundai License
Production: Hyundai 91A heavy truck (produced under license in South
Korea). Hyundai Aero Bus for the Korean domestic market.
Construction Vehicles: Concrete mixer trucks. Dump trucks, including the
Mitsubishi FV413JD model. Special Applications: Fire trucks. Armored
security vehicles for Japanese law enforcement. The engine was replaced
in production by the 8DC9, 8DC10, and 8DC11 series, as well as by
turbocharged engines such as the 8M20 and 6M70 series.
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