Mitsubishi S3Q2 Specifications
| Engine Model: Mitsubishi S3Q2 |
| Engine Type: 4-cycle inline 3-cylinder OHV forced-feed lubrication liquid-cooled diesel |
| Total Displacement: 114.7 cu.in (1.88 L) |
| Rated Engine Power: 31.3-40.5 Hp (23.3-30.2 kW) at 2400 rpm |
| Fuel System Type: Indirect fuel injection |
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The Mitsubishi S3Q2 is a versatile
three-cylinder diesel engine, engineered to provide a robust balance of
power, compact size, and operational reliability for demanding
industrial and construction applications. Available in both naturally
aspirated and turbocharged variants, this 1.879-liter power unit is
designed to meet intermediate emission standards while maintaining
mechanical simplicity and durability.
As an Indirect Injection (IDI) engine with a swirl pre-combustion
chamber, it delivers smooth combustion characteristics, reduced noise,
and excellent cold-start performance. The turbocharged "T" variant
offers a significant increase in power and torque density, making it
suitable for more power-intensive machinery. Its design prioritizes
structural rigidity and serviceability, with a focus on enduring the
variable loads and harsh environmental conditions present in compact
construction equipment. The S3Q2 is recognized for its dependable power
delivery and has been widely adopted as a prime mover in globally
recognized machinery platforms.
Manufacturer: Mitsubishi Heavy Industries Engine and Turbocharger, Ltd.
(MHIET).
Engine Model: S3Q2 (Naturally Aspirated), S3Q2-T (Turbocharged).
Engine Type: 4-cycle, water-cooled, vertical inline, indirect injection
diesel.
Aspiration: Naturally aspirated or Turbocharged (T model).
Emission Compliance: Conforms to US EPA Tier 4 Interim (Stage 3B) / EU
Stage IIIA regulations for common industrial variants.
Management System: Mechanical fuel injection with mechanical governor.
Some advanced variants may include electronic governing for emission
optimization.
Number of Cylinders: 3.
Bore: 88 mm (3.465 in).
Stroke: 103 mm (4.055 in).
Displacement: 1.879 L (1879 cc) (114.7 cu in).
Compression Ratio: 22:1.
Firing Order: 1-3-2.
Rotation Direction: Counter-clockwise when viewed from the flywheel
side.
Maximum Net Power Output (Naturally Aspirated): 23.3 kW (31.3 hp) at
2,300 rpm.
Maximum Net Power Output (Turbocharged S3Q2-T): 30.2 kW (40.5 hp) at
2,400 rpm.
Maximum Net Torque (Turbocharged): 120 Nm (88.5 lb-ft) at 1,600 rpm.
Rated Speed: 2,300-2,400 rpm (application dependent).
Idle Speed: 850 ±50 rpm.
The cylinder block is a rigid, single-piece casting manufactured from
high-strength gray iron. It employs a closed-deck design, where the
upper section of the cylinder bores is integrated into a solid, unbroken
deck. This construction provides maximum structural integrity to contain
combustion pressures and minimizes cylinder bore distortion under load.
The cylinder bores are precision-honed directly into the block material,
utilizing a linerless design for efficient heat transfer to the
surrounding coolant jackets. The crankshaft is a forged steel component,
supported by four main bearings. This four-bearing support system for a
three-cylinder crank provides excellent stability, effectively managing
the inherent rocking couple and contributing to smooth engine operation.
Connecting rods are forged steel, fitted with replaceable precision
bearing shells at the crankpin end. The piston pin is a press-fit in the
connecting rod small end. Pistons are aluminum alloy, designed with a
specific crown shape compatible with the IDI swirl chamber system. The
piston ring pack consists of two chrome-plated compression rings and a
three-piece oil control ring.
A single-piece cast iron cylinder head is utilized, secured to the block
with high-tensile studs and nuts. The head is designed to accommodate
one intake and one exhaust valve per cylinder. Valve seat inserts are
manufactured from hardened, heat-resistant alloy to ensure longevity
under continuous thermal stress. The valve train operates on an overhead
valve (OHV) principle, with the camshaft positioned in the cylinder
block.
The camshaft is gear-driven from the crankshaft and actuates the valves
via solid pushrods and rocker arms. Rocker arms are mounted on a
stationary shaft fastened to the cylinder head. Valve clearance is set
and maintained by a screw and locknut adjustment on each rocker arm,
requiring periodic manual inspection and adjustment as a core
maintenance task. The cylinder head incorporates the indirect injection
pre-combustion (swirl) chamber for each cylinder, which includes a glow
plug for cold starting assistance.
The engine employs a mechanical, inline pump-line-nozzle fuel injection
system. Core components include a mechanical fuel lift pump, an inline
injection pump with individual pumping elements for each cylinder,
high-pressure fuel lines, and injectors. The injection pump is a
jerk-pump design, driven by the engine's gear train. It supplies fuel at
high pressure to pintle-type nozzles that discharge into the
pre-combustion swirl chamber.
A mechanical centrifugal governor, integral to the injection pump,
regulates engine speed by controlling the position of the fuel rack. The
system is calibrated for precise fuel delivery to meet specific power
and emission requirements. Fuel filtration is critical, involving both a
primary sedimentor/water separator and a secondary fine filter to
protect the precision components of the injection pump and injectors.
Lubrication is provided by a forced-feed, full-flow wet sump system. A
gear-type oil pump, driven directly from the crankshaft, draws oil from
the sump through a pickup tube equipped with a strainer screen.
Pressurized oil is routed through a full-flow, spin-on cartridge oil
filter.
After filtration, oil enters the main oil gallery in the block,
supplying the crankshaft main and connecting rod bearings, the camshaft
bearings, and the valve gear via internal passages and hollow pushrods.
In the turbocharged (T) variant, an additional oil feed and drain line
services the turbocharger center bearing. The specified engine oil is
API CF-4 grade or higher. Total oil capacity, including the filter, is
5.5 liters (5.8 US qt). The oil pan is a stamped steel component.
Cooling is managed by a pressurized, pump-circulated liquid system. A
centrifugal water pump, driven by a V-belt from the crankshaft pulley,
provides coolant circulation. System operating temperature is regulated
by a wax-pellet type thermostat housed in the water outlet housing. Heat
rejection occurs via a tube-and-fin radiator; the cooling fan is mounted
on the engine and is V-belt driven.
The cooling system requires a mixture of ethylene-glycol antifreeze and
clean, deionized water, generally in a 50/50 ratio for full corrosion
protection and freeze resistance. Total cooling system capacity is 4.5
liters (4.8 US qt) for the engine side, excluding the radiator and
external hose volume.
Intake System: Consists of an air cleaner, and on the turbocharged
(S3Q2-T) model, a turbocharger and intake piping. The naturally
aspirated version uses a simple intake manifold.
Exhaust System: Comprises an exhaust manifold. On the turbocharged
model, the manifold feeds exhaust gas to the turbocharger turbine,
exiting via a downpipe. The system may include an oxidation catalyst to
meet emission standards.
Electrical System: Operates on a 12V system. A 12V starter motor and a
12V alternator are standard. The engine incorporates a glow plug system
for each cylinder, controlled by a key-switch or timer module for cold
starting. An electric stop solenoid acts on the injection pump rack.
Governor: A mechanical centrifugal governor is standard, integrated
within the fuel injection pump.
Length (Front Face of Block to Flywheel Housing): 608 mm (23.94 in).
Width (Overall): 540 mm (21.26 in).
Height (Overall, from sump to valve cover): 696 mm (27.40 in).
Dry Weight (with standard accessories, Turbo model): 160 kg (353 lb).
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 operating hours. Air Cleaner
Element Service: Clean or replace based on restriction indicator;
inspect daily in dusty environments. Valve Clearance Adjustment: Check
and adjust every 500 operating hours.
Coolant Replacement: Drain, flush, and refill every 2,000 operating
hours or every two years. Fan Belt Tension Check/Adjustment: Inspect and
adjust tension every 250 hours; replace belts showing signs of wear,
glazing, or cracking. Fuel Injection System Inspection: Have injection
pressure and spray pattern checked by a specialist every 1,500 hours.
Cylinder Head Nuts: Tighten in the specified multi-step crisscross
sequence to a final torque of 108-118 Nm (80-87 lb-ft).
Main Bearing Cap Bolts: 88-98 Nm (65-72 lb-ft).
Connecting Rod Cap Bolts: 59-69 Nm (44-51 lb-ft).
Flywheel to Crankshaft Bolts: 108-118 Nm (80-87 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).
Oil Filter Cartridge: Hand-tighten plus 3/4 turn after the sealing
gasket contacts the base.
The Mitsubishi S3Q2 engine, particularly the turbocharged S3Q2-T
variant, is a cornerstone power plant for a specific class of compact
construction machinery, most notably in Caterpillar's mini-excavator
line.
Its primary applications include: Compact Excavators: Caterpillar 301.5,
301.6, 301.8, 303.5C, 303.5CR, 303.5E, 303E, 304C, 304D, and 304E CR
mini-excavators. Other Construction Equipment: Various small soil
compactors, trenchers, and mobile hydraulic power packs from multiple
manufacturers. Agricultural Applications: Used in some compact
agricultural tractors and specialized farming machinery requiring a
dependable, turbocharged diesel engine.
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