Mitsubishi 4D55 Specifications
| Engine Model: Mitsubishi 4D55 |
| Engine Type: 4-cycle inline 4-cylinder SOHC 8-valve liquid-cooled diesel |
| Total Displacement: 143 cu.in (2.34 L) |
| Rated Engine Power: 75 Hp (56 kW) at 4200 rpm |
| Fuel System Type: Indirect injection |
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The Mitsubishi 4D55 is a 2.3-liter, 4-cylinder diesel
engine introduced in the early 1980s as part of the Astron family. It
represented Mitsubishi’s first foray into modern passenger-car diesel
engineering and achieved distinction as the first diesel engine in a Japanese
passenger car equipped with a turbocharger. The 4D55 powered a generation of
vehicles including the early Pajero (Montero), L200 (Forte), and the Dodge Ram
50, establishing a reputation for durability and mechanical simplicity.
Its indirect injection system with a swirl chamber provided refined operation
for its era, while the turbocharged variant offered performance that broadened
diesel appeal beyond commercial applications. The engine’s architecture
emphasizes serviceability, with a timing belt driving the single overhead
camshaft and a robust cast-iron construction that contributed to its widespread
adoption across Mitsubishi’s light truck and SUV range.
Engine Type: 4-stroke, inline 4-cylinder, water-cooled diesel engine.
Displacement: 2,346 cc (2.3 L; 143 cu.in).
Bore: 91.1 mm (3.587 in).
Stroke: 90.0 mm (3.543 in).
Compression Ratio: 21.0:1.
Firing Order: 1-3-4-2.
Valvetrain: SOHC (single overhead camshaft), 2 valves per cylinder, timing belt
drive.
Aspiration: Naturally aspirated.
Maximum Power: 56 kW (75 hp) at 4,200 rpm.
Maximum Torque: 138 Nm (102 lb-ft) at 2,500 rpm.
Combustion System: Indirect injection with swirl chamber (Ricardo-type
pre-combustion chamber).
Compression Pressure
Standard (new): 3.04 MPa (441 psi)
Minimum service limit: 2.26 MPa (327 psi)
Maximum permissible variation between cylinders: 0.10 MPa (15 psi)
The cylinder block is constructed from gray cast iron,
providing a rigid foundation with excellent vibration damping characteristics.
The block features a deep-skirt design where the cylinder walls extend below the
crankshaft centerline, enhancing structural rigidity under high cylinder
pressures. Five main bearings support the forged steel crankshaft, with bearing
caps secured by vertical bolts.
The cylinders are cast directly into the block without replaceable liners,
finished with a plateau honing pattern to promote oil retention and ring
seating. A cast iron oil pan forms the lower sump, sealed to the block with a
fiber-reinforced gasket. The block incorporates a side-mounted mechanical fuel
injection pump mounting flange and features cast bosses for the engine mounting
brackets. Coolant passages surround each cylinder bore to ensure uniform thermal
distribution, with a water jacket extending the full height of the cylinders.
The cylinder head is manufactured from gray cast iron,
chosen for thermal stability and resistance to cracking under the elevated
temperatures associated with indirect injection combustion. The head employs a
cross-flow design with intake ports on the right side and exhaust ports on the
left side for the standard transverse engine mounting configuration.
Each cylinder features a separate swirl chamber pre-combustion insert made from
heat-resistant steel, pressed into the head. The single overhead camshaft is
supported by four bearing journals and actuates eight valves through steel
rocker arms with integral adjusting screws for valve clearance. Hydraulic
lifters were not employed; manual adjustment using a locknut and set-screw
arrangement is required at prescribed intervals.
Number of Valves: 8 total (2 per cylinder).
Intake Valve Diameter: 39.0 mm (1.535 in).
Exhaust Valve Diameter: 33.0 mm (1.299 in).
Valve Stem Diameter: 8.0 mm (0.315 in) for both intake and exhaust.
Valve Seat Inserts: Induction-hardened seats machined directly into the cylinder
head for intake; heat-resistant alloy steel inserts for exhaust.
Valve Clearance (hot engine, at operating
temperature)
Intake: 0.25 mm (0.010 in).
Exhaust: 0.25 mm (0.010 in).
The fuel system employs indirect injection with a
swirl-chamber combustion process. A mechanical in-line injection pump,
manufactured by Diesel Kiki or Zexel depending on production date, is mounted to
the left side of the cylinder block and driven by the timing belt. The pump
incorporates a mechanical governor to regulate fuel delivery according to engine
speed and load.
High-pressure fuel lines deliver injection pulses to nozzle holders, each
containing a pintle-type nozzle with an opening pressure of approximately
11.8-12.7 MPa (1,710-1,840 psi). The swirl chamber pre-combustion chambers
promote complete mixing of fuel and air, reducing combustion noise and
permitting the use of a lower compression ratio than direct injection
contemporaries. A hand-operated primer pump is integrated into the fuel filter
housing for priming the system after filter replacement.
Injectors: Pintle-type nozzle with spring-loaded holder; opening pressure
11.8-12.7 MPa (1,710-1,840 psi). Fuel Filtration: Single replaceable
cartridge-type fuel filter with integral water separator and sediment bowl.
Injection Pump Type: In-line mechanical pump, 4-cylinder, with mechanical
governor and automatic timing advance.
The lubrication system utilizes a gear-type oil pump
mounted within the front timing cover and driven directly by the crankshaft. The
pump draws oil from a baffled steel sump through a strainer screen and delivers
it to a full-flow disposable cartridge oil filter mounted externally on the
cylinder block. From the filter, oil is distributed through main galleries to
the crankshaft main bearings, connecting rod bearings, camshaft bearings, and
valve train components.
A pressure relief valve maintains system pressure within specified limits.
Turbocharged variants incorporate a water-cooled oil cooler mounted between the
oil filter and the engine block, using engine coolant to maintain oil
temperature under high load.
Oil Pump Type: Gear-type, crankshaft-driven.
Oil Pressure (hot, at 3,000 rpm): 294-392 kPa (43-57 psi).
Oil Pressure (hot, idle): 49 kPa (7 psi) minimum.
Oil Capacity (with filter, naturally aspirated): 5.5 L (5.8 US qt).
Oil Capacity (with filter, turbocharged with oil cooler): 6.5 L (6.9 US qt).
Oil Specification: API CD, CE, or CF; SAE 15W-40 or 20W-50 depending on ambient
temperature range.
The cooling system employs a belt-driven centrifugal
water pump mounted to the front of the cylinder block. Coolant flows from the
radiator through the pump, then through the cylinder block water jacket
surrounding the cylinders, upward into the cylinder head, and returns to the
radiator through the thermostat housing. A wax-pellet thermostat located at the
coolant outlet regulates operating temperature by controlling flow to the
radiator. The system includes a cross-flow radiator with a pressure-type filler
cap rated at 88-98 kPa (13-14 psi). Turbocharged variants incorporate a separate
oil cooler circuit integrated into the coolant flow path.
Water Pump Type: Belt-driven centrifugal pump with cast iron housing and pressed
steel impeller. Coolant Capacity (engine and radiator): 7.5-8.5 L (7.9-9.0 US
qt) depending on heater core and oil cooler configuration. Thermostat Opening
Temperature: 76.5-80.0 °C (170-176 °F). Thermostat Fully Open Temperature: 90 °C
(194 °F). Coolant Specification: Ethylene-glycol based antifreeze with corrosion
inhibitors; 30-50% concentration.
| Intake and Exhaust Systems |
Intake System: Naturally aspirated variants draw air
through a replaceable paper-element air cleaner and a cast aluminum intake
manifold. Turbocharged variants incorporate a single Mitsubishi TD04 series
turbocharger mounted to the exhaust manifold, with a water-cooled bearing
housing and integral wastegate. Boost pressure is regulated to approximately
59-69 kPa (8.6-10.0 psi) at full load. A charge-air cooler was not utilized in
factory configurations.
Exhaust System: Cast iron exhaust manifold with integrated mounting flange for
turbocharger on boosted variants. The manifold is designed to accommodate
thermal expansion through slotted bolt holes at the cylinder head flange.
| Electrical and Starting System |
Electrical System: 12 V negative-ground electrical
architecture. Starter motor is a reduction-gear type mounted to the transmission
bellhousing side of the engine. Glow plug system uses pencil-type ceramic or
steel-sheathed glow plugs in each pre-combustion chamber, controlled by a glow
timer relay with post-glow function for reduced cold-start emissions.
Starting System: Glow plug activation for cold starts; glow duration dependent
on coolant temperature, ranging from 1.5 to 8.0 seconds.
Length (front of fan to rear of flywheel housing): 760
mm (29.9 in).
Width (overall, including injection pump and exhaust manifold): 580 mm (22.8
in).
Height (from oil pan rail to top of valve cover): 710 mm (28.0 in).
Dry Weight (naturally aspirated, complete engine with flywheel and manifolds):
185 kg (408 lb).
Dry Weight (turbocharged, with oil cooler and turbocharger assembly): 195 kg
(430 lb).
Engine Oil: API CD, CE, or CF; SAE 15W-40, 10W-30,
20W-50.
Oil Change Interval: 5,000 km (3,000 mi) for severe service.
Oil Change Interval: 10,000 km (6,000 mi) for normal service.
Coolant Capacity: 7.5-8.5 L (7.9-9.0 US qt).
Coolant Change Interval: 24 months or 40,000 km (25,000 mi).
Fuel Filter Replacement: 20,000 km (12,000 mi) or 12 months.
Air Filter Replacement: 20,000 km (12,000 mi); more frequent under dusty
conditions.
Timing Belt Replacement: 100,000 km (60,000 mi) or 60 months.
Valve Clearance Inspection: 20,000 km (12,000 mi).
Idle Speed (manual transmission, neutral): 700-750 rpm.
Idle Speed (automatic transmission, in drive): 700-750 rpm.
Glow Plug Inspection: 40,000 km (25,000 mi); resistance check and visual
inspection for swelling.
Cylinder Head Bolts (cold engine, M12): 105-115 Nm
(77-85 lb-ft)
Main Bearing Cap Bolts (M12): 75-85 Nm (55-63 lb-ft)
Connecting Rod Cap Bolts (M10): 45-48 Nm (33-35 lb-ft)
Flywheel Bolts (M12): 130-140 Nm (96-103 lb-ft)
Camshaft Sprocket Bolt: 60-70 Nm (44-52 lb-ft)
Rocker Arm Shaft Hold-down Bolts: 25-30 Nm (18-22 lb-ft)
Injection Pump Drive Gear Nut: 80-90 Nm (59-66 lb-ft)
Injection Nozzle Holder: 55-65 Nm (41-48 lb-ft)
Intake Manifold Bolts: 20-25 Nm (15-18 lb-ft)
Exhaust Manifold Bolts: 20-25 Nm (15-18 lb-ft)
Turbocharger Mounting Bolts: 35-45 Nm (26-33 lb-ft)
Oil Pan Bolts: 8-12 Nm (6-9 lb-ft)
Valve Cover Nuts: 5-7 Nm (4-5 lb-ft)
Glow Plugs: 15-20 Nm (11-15 lb-ft)
Engine Mount Bracket to Block: 40-50 Nm (30-37 lb-ft)
Crankshaft Pulley Bolt: 180-200 Nm (133-148 lb-ft)
Water Pump Bolts: 15-20 Nm (11-15 lb-ft)
Mitsubishi Pajero / Montero: First generation (L040
series, 1982-1990) with 4D55 and 4D55T engines. Mitsubishi L200 / Forte: Second
generation (L040 series pickup, 1978-1986) with naturally aspirated and
turbocharged variants. Mitsubishi Delica / Starwagon: L300 series (1982-1986)
van and wagon variants. Mitsubishi Galant: E15A series (1982-1983) selected
markets; one of the first Japanese passenger cars with a factory turbocharged
diesel.
Dodge Ram 50: 1983-1986 model years, badge-engineered version of the Mitsubishi
L200. Plymouth Arrow Truck: 1983-1984 model years, badge-engineered variant with
4D55T. Ford Courier: Selected Asian and Oceanic markets where the
Mitsubishi-sourced diesel option was offered.
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