Mitsubishi 4D34 Specifications
| Engine Model: Mitsubishi 4D34 |
| Engine Type: 4-cycle inline 4-cylinder naturally aspirated liquid-cooled diesel |
| Total Displacement: 238.5 cu.in (3.9 L) |
| Rated Engine Power: 115-130 Hp (85-96 kW) at 2900 rpm |
| Fuel System Type: Direct fuel injection |
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The Mitsubishi 4D34 is a medium-displacement
inline-four diesel engine designed for use in light- and medium-duty
commercial vehicles, industrial machinery, agricultural equipment, and
auxiliary power units. As part of the Mitsubishi 4D3 family, it
represents an evolution of the earlier 4D31 and 4D32 series,
incorporating improved combustion characteristics, stronger internal
architecture, higher torque stability at low engine speeds, and long
service life under continuous duty.
The engine is widely known for reliability, mechanical simplicity,
rugged cast-iron construction, and strong mid-range pulling power. It
became one of the most widely used engines in Mitsubishi Fuso Canter
trucks, export vehicles, and industrial platforms requiring durability,
low operating cost, and easy field serviceability.
The 4D34 gained a reputation for long operational life in harsh
environments, including high-dust, heavy-load, and high-temperature
conditions. It has a conservative design philosophy that prioritizes
mechanical strength, stable cooling, reliable lubrication, and ease of
maintenance.
The combination of gear-driven timing, direct-injection fuel delivery,
and simple electrical systems makes the 4D34 suitable for areas with
limited service infrastructure and variable fuel quality. Many engines
remain in service after hundreds of thousands of km or thousands of
industrial hours.
The Mitsubishi 4D34 is a four-stroke, water-cooled, inline four-cylinder
diesel engine. Total displacement is about 3,908 cc (238.5 cubic
inches). Bore is 104 mm (4.09 inches) and stroke is 115 mm (4.53
inches). This long-stroke layout improves torque production at low and
mid-range engine speeds and enhances fuel economy under steady load.
Compression ratio varies between 17.0:1 and 18.0:1 depending on version.
Power output depends on model:
- Naturally aspirated versions produce about 115-130 Hp (85-96 kW) at
around 2,900 rpm.
- Turbocharged versions produce about 135-155 Hp, and
intercooler-equipped turbo variants may reach up to 165 Hp.
Peak torque ranges from 275-430 Nm at 1,600-2,000 rpm depending on
configuration. Idle speed is 700-750 rpm. Maximum governed speed for
truck applications is usually around 3,000-3,200 rpm.
The firing order is 1-3-4-2. The crankshaft is forged steel, fully
counterweighted, and supported by five large main bearings. Pistons are
cast aluminum alloy with reinforced crowns and combustion bowls.
Two compression rings and one oil-control ring form the ring pack.
Piston cooling oil jets may be installed on heavy-duty versions.
Connecting rods are forged steel with replaceable bearings. The camshaft
is located in the block and driven by a gear train, ensuring lifetime
timing stability with no belt service required.
The cylinder block is cast iron with deep ribbing for rigidity and
vibration reduction. The internal coolant jackets are shaped to
distribute heat evenly around the cylinder bores. Oil passages supply
lubrication to main bearings, camshaft bearings, piston cooling jets,
and rocker assemblies.
The crankcase is designed for high strength and long service life under
heavy mechanical loads. The block is compatible with various industrial
accessory layouts including hydraulic pumps, vacuum pumps, air
compressors, and PTO systems.
The cylinder head is cast iron to maintain dimensional stability under
high thermal loads. Variants include direct-injection and earlier
pre-combustion-chamber designs. The valve train uses pushrods and rocker
arms. Valve lash is manually adjustable.
Cold settings are 0.25-0.30 mm for intake valves and 0.35-0.40 mm for
exhaust valves. The intake and exhaust ports are shaped to produce
strong swirl and efficient fuel-air mixing. Valve seats are hardened for
long life in severe duty.
The 4D34 uses a mechanical direct-injection system in most versions. A
mechanical lift pump draws fuel from the tank. Fuel passes through a
primary sediment bowl or water separator, then through a secondary fine
paper filter.
A high-pressure inline or rotary pump meters the fuel and controls
timing. Injection pressures generally range from 250-350 bar. Injectors
are multi-hole types that atomize fuel directly into the piston bowl.
Early variants may use indirect injection with pintle nozzles supplying
pre-combustion chambers.
Fuel system maintenance:
- Primary and secondary filters every 10,000-15,000 km
- Injector servicing every 40,000-60,000 km
- Injection-pump timing inspection at major service intervals
- Water-separator draining as needed
The lubrication system is a full-pressure wet-sump design using a
gear-driven oil pump. Oil is drawn through a pickup screen in the sump,
then routed through a full-flow spin-on filter.
Main oil galleries deliver lubrication to crankshaft main bearings,
connecting-rod journals, camshaft bearings, rocker arms, and
turbocharger bearings on turbo models. Some variants include
piston-cooling oil jets.
Oil capacity is about 8-10 liters (8.4-10.5 US quarts). Normal pressure
is around 300-450 kPa at operating speed and 100-150 kPa at idle.
Recommended oil viscosity is SAE 15W-40 or 20W-50 diesel oil meeting API
CF or higher.
Cooling is provided by a forced-circulation, closed-loop liquid cooling
system. A belt-driven centrifugal water pump circulates coolant through
the block, head, and radiator.
A thermostat begins opening at about 82°C and is fully open near 95°C.
Coolant capacity ranges from 9-12 liters. System pressure is 70-90 kPa.
A 50/50 mix of ethylene glycol and water is recommended.
| Intake and Exhaust Systems |
Automotive versions use dry-element air filters, while industrial
versions may include oil-bath filters or cyclone pre-cleaners. The
intake manifold is cast aluminum or cast iron. Cold-start aids include
glow plugs and intake heaters.
The exhaust manifold is cast iron; turbocharged versions mount the turbo
directly to the manifold. Industrial exhaust systems may include spark
arrestors, heavy mufflers, or vertical stacks.
Electrical systems are either 12-volt or 24-volt depending on
application. Alternators range from 40-70 A. Starter motors are rated
from 2.0-3.0 kW. Glow-plug systems assist cold starts. Wiring harnesses
are designed for vibration resistance and long life.
The 4D34 supports multiple auxiliary systems, including hydraulic pumps,
vacuum pumps, power-steering pumps, air compressors, PTO drives, and
marine cooling systems.
- Length: 780-820 mm
- Width: 650-700 mm
- Height: 820-860 mm
- Dry weight: 260-320 kg depending on configuration
- Engine oil and filter: 5,000-7,500 km
- Fuel filters: 10,000-15,000 km
- Air filter: 8,000-12,000 km
- Coolant: every 30,000 km or 2 years
- Valve lash: every 15,000-20,000 km
- Injectors: every 40,000-60,000 km
- Compression test: every 100,000 km
- Cylinder head bolts: 120-140 Nm
- Main bearing caps: 120-140 Nm
- Connecting-rod bolts: 55-65 Nm
- Flywheel bolts: 110-130 Nm
- Crank pulley bolt: 180-210 Nm
- Oil drain plug: 35-45 Nm
- Injector hold-downs: 20-25 Nm
- Glow plugs: 10-15 Nm
The Mitsubishi 4D34 is widely used in Mitsubishi Fuso Canter trucks,
export-market cab-over vehicles, buses, generator sets, agricultural
machines, forklifts, construction equipment, irrigation pumps, and
marine auxiliary drives.
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