Mitsubishi S4Q Specifications
| Engine Model: Mitsubishi S4Q |
| Engine Type: 4-cycle inline 4-cylinder liquid-cooled diesel |
| Total Displacement: 152.9 cu.in (2.51 L) |
| Rated Engine Power: 51 Hp (38.2 kW) at 2500 rpm |
| Fuel System Type: Indirect injection |
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The Mitsubishi S4Q is a 2.5-liter inline
4-cylinder naturally aspirated diesel engine from the SQ Series,
produced by Mitsubishi Heavy Industries. Designed as a compact
industrial powerplant, this engine has been widely deployed in mid-sized
forklifts, excavators, generator sets, and agricultural equipment across
global markets. The Mitsubishi S4Q employs an indirect injection system
with a swirl chamber combustion design, a configuration selected to
provide smooth operation, low noise output, and reduced vibration
compared to direct injection alternatives of its era.
The engine features a mechanical in-line pump fuel system, water-cooled
forced circulation cooling, and a counterclockwise rotation direction
when viewed from the flywheel end. The S4Q was also produced in a
turbocharged configuration designated S4Q2-T, offering increased power
output for applications demanding higher performance within the same
displacement.
Engine Family: Mitsubishi SQ Series
Engine Code: S4Q (also S4Q2 for later variants)
Configuration: Inline 4-cylinder, 4-stroke, water-cooled diesel
Displacement: 2505 cc (152.9 cu.in)
Bore: 88.0 mm (3.46 in)
Stroke: 103.0 mm (4.06 in)
Compression Ratio: 22.0:1
Firing Order: 1-3-4-2
Combustion System: Indirect injection, swirl chamber type
Aspiration: Naturally aspirated (S4Q); turbocharged (S4Q2-T)
Maximum Power (Naturally Aspirated): 38.2 kW (51 hp) at 2500 rpm
Maximum Power (Variable Speed Industrial): 34.6 kW (47 hp) at 2200 rpm
Torque: 420 Nm (310 lb-ft) at 1800 rpm (aftermarket specification)
Idle Speed: Variable based on governor setting and application
Emission Standard: EU Stage IIIA; suitable for non-regulated
applications
The cylinder block is constructed from ribbed thin-wall cast iron, a
design selected to add strength and durability while maintaining
controlled weight. The block incorporates a cast internal crankcase
breather system that reduces emissions by recirculating blow-by gases.
The bearing surfaces are oversized to distribute mechanical loads across
a larger area, reducing bearing loads and extending service life. The
block features a deep-skirt design with five main bearings supporting
the forged or cast iron crankshaft.
The cylinder bores are machined directly into the parent material with a
honed finish. The block incorporates integral mounting points for the
fuel injection pump, water pump, and application-specific equipment such
as hydraulic pump drives for forklift and excavator installations. The
oil pan capacity varies by application, ranging from 6.5 to 8.2 liters
(6.9 to 8.7 qt) depending on the specific oil pan configuration.
The cylinder head is manufactured from cast iron using a cross-flow
design, with the intake manifold positioned on one side and the exhaust
manifold on the opposite side. The overhead valve (OHV) arrangement
employs pushrods and rocker arms actuated by a camshaft located within
the cylinder block. Two valves per cylinder are provided, for a total of
eight valves across the engine.
Valve seats are pressed into the head, with exhaust seats receiving
hardened facing for temperature durability. Valve clearances are
adjustable using threaded adjusters and locknuts. Cold valve clearance
specification is 0.25 mm (0.0098 in) for both intake and exhaust valves.
The cylinder head gasket is a steel construction designed to withstand
the compressive loads of the 22:1 compression ratio.
The fuel system employs an indirect injection configuration with a swirl
chamber (Ricardo-type) combustion system, producing a controlled
air-fuel mixing process prior to ignition. A mechanical in-line
injection pump, driven by the engine timing gears, delivers fuel to
individual injection nozzles. The system utilizes a pump-line-nozzle
architecture, where high-pressure lines connect the injection pump to
each cylinder’s injector.
A mechanical governor maintains consistent engine speed under varying
load conditions, a critical feature for industrial applications where
load fluctuates during operation. A mechanical feed pump supplies fuel
from the tank to the injection pump. The system includes a fuel filter
with a replaceable element and a water separator. Glow plugs are
provided for cold starting assistance in low-temperature conditions.
The lubrication system is a forced-feed, full-pressure wet-sump
configuration utilizing a gear-type oil pump. The pump draws oil through
a fixed mesh pickup screen located in the oil pan and delivers it
through a full-flow spin-on oil filter mounted on the cylinder block.
System capacity varies by oil pan configuration, ranging from 6.5 to 8.2
liters (6.9 to 8.7 qt).
Recommended oil viscosity is SAE 10W-30 or 15W-40 meeting API Class CD
or higher specifications for diesel engines. Oil pressure at operating
speed is maintained within specified ranges. A pressure relief valve
integrated into the oil pump housing limits maximum system pressure. The
oil pan incorporates baffles to maintain oil pickup when the engine is
operating at inclined angles, a feature particularly relevant for
forklift and excavator applications.
The cooling system is a water-cooled forced circulation configuration
utilizing a centrifugal water pump driven by the engine. The pump
includes a thermostat that regulates coolant temperature by bypassing
flow to the radiator until operating temperature is reached. The system
is designed for freshwater cooling with a radiator.
The raw water version for marine applications incorporates a heat
exchanger system. Coolant specified is ethylene glycol-based mixed with
distilled water at appropriate ratio for the expected operating
environment. The cooling system includes a fan mounted on the water pump
pulley, driven by the same belt as the water pump.
Electrical System: 12-volt system rated at 50 amperes. Starter motor
rated at 2.0 kW.
Starting System: Glow plugs for cold start pre-heating. Requires 12V
battery.
Rotation Direction: Counterclockwise when viewed from the flywheel end
(ISO 1204 standard).
Flywheel Housing: SAE #4 configuration with 7.5 inch housing.
Intake System: Dry-type air filter with replaceable paper element.
Exhaust System: Cast iron exhaust manifold with single outlet.
Engine Management: Mechanical governor only; no electronic engine
management.
Overall Length: 708-781 mm (27.9-30.7 in) depending on accessory
configuration.
Overall Width: 493-558 mm (19.4-22.0 in).
Overall Height: 631-714 mm (24.8-28.1 in).
Dry Engine Weight (without coolant, oil, and accessories): 195 kg (430
lb).
Intake Valve Clearance: 0.25 mm (0.0098 in)
Exhaust Valve Clearance: 0.25 mm (0.0098 in)
Injection Pump Timing: static timing 13° BTDC
Engine Oil Change: Every 250 operating hours.
Oil Filter Replacement: Every oil change (250 hours).
Fuel Filter Replacement: Replace primary and secondary filter elements
every 500 hours.
Air Cleaner Element Service: Clean or replace based on restriction
indicator.
Valve Clearance Adjustment: Check and adjust every 500 operating hours.
Coolant Replacement: Drain, flush, and refill every 2,000 hours or every
two years.
Fan Belt Tension Check/Adjustment: Inspect and adjust tension every 250
hours.
Fuel Injection System Inspection: Check every 1,500 hours.
Cylinder Head Bolts (M10): 88-98 Nm (65-72 lb-ft)
Connecting Rod Cap Nuts: 54-59 Nm (40-44 lb-ft)
Main Bearing Cap Bolts: 108-118 Nm (80-87 lb-ft)
Flywheel Bolts: 127-137 Nm (94-101 lb-ft)
Engine Oil Drain Plug: 44 Nm ± 5 Nm (32.5 lb-ft ± 4 lb-ft)
Fuel Injector Holder: 59-69 Nm (44-51 lb-ft).
Glow Plugs: 15-20 Nm (11-15 lb-ft).
Oil Pan Drain Plug: 49-59 Nm (36-44 lb-ft).
Forklifts: Mitsubishi FD20, FD25, FD30 series; Caterpillar DP20, DP25,
DP30; various other material handling equipment.
Excavators: Hanix, Terex, Schaeff mini-excavators and compact
excavators; Kato and other Japanese mini-excavator brands.
Construction Equipment: Wheel loaders, road rollers, trenchers,
compaction equipment.
Generator Sets: Stationary and portable generator sets in the 20-30 kVA
range; industrial prime and standby power units.
Agricultural Equipment: Tractors, combine harvesters, tillers, crop
sprayers for mid-sized farm machinery.
Marine Applications: Leisure marine propulsion (auxiliary engines) and
marine auxiliary power.
Commercial Vehicles: Light to medium-duty delivery trucks, refrigerated
vans; Mitsubishi vehicles including Triton/L200 pickups and Delica vans.
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