Mitsubishi S3L2 Specifications
| Engine Model: Mitsubishi S3L2 |
| Engine Type: 4-cycle inline 3-cylinder naturally aspirated liquid-cooled diesel |
| Total Displacement: 80.4 cu.in (1.32 L) |
| Rated Engine Power: 28.4 Hp (21.2 kW) at 3000 rpm |
| Fuel System Type: Direct or indirect fuel injection |
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The Mitsubishi S3L2 is a compact,
three-cylinder diesel engine recognized for its robust construction and
dependable performance in demanding light industrial applications. This
1.318-liter power unit is engineered to deliver a balance of power,
torque, and durability within a constrained physical envelope, making it
a preferred choice for mini-excavators and compact construction
machinery.
The engine is available in distinct configurations, featuring either a
traditional Indirect Injection (IDI) system with a swirl pre-combustion
chamber for smooth operation and excellent cold starting, or a more
modern Direct Injection (DI) system for improved fuel efficiency and
power density. Its design prioritizes reliability under variable load
conditions and ease of maintenance in field environments. Modern
iterations of the S3L2 platform incorporate advanced engineering to meet
stringent emission regulations, including EU Stage V, through precise
fuel management and integrated exhaust after-treatment systems.
Manufacturer: Mitsubishi Heavy Industries Engine and Turbocharger, Ltd.
(MHIET).
Engine Model: S3L2.
Engine Type: 4-cycle, water-cooled, vertical inline diesel.
Combustion System: Indirect Injection (Swirl Chamber) or Direct
Injection.
Model designation specifies the type (e.g., S3L2-DI).
Aspiration: Naturally aspirated.
Number of Cylinders: 3.
Bore: 78 mm (3.071 in).
Stroke: 92 mm (3.622 in).
Displacement: 1.318 L (1318 cc) (80.4 cu in).
Compression Ratio: Indirect Injection: 22:1. Direct Injection: 18:1.
Firing Order: 1-2-3.
Rotation Direction: Counter-clockwise when viewed from the flywheel
side.
Maximum Gross Power Output: Up to 21.2 kW (28.4 hp) at 3,000 rpm for
variable-speed industrial models.
Constant-speed generator variants produce 11.3 kW (15.2 hp) at 1,500
rpm.
Maximum Gross Torque: 76.3 Nm (56.3 lb-ft) at 1,800-2,000 rpm
(representative for DI variants).
Maximum Governed Speed: 3,000 rpm for industrial applications; 1,500 or
1,800 rpm for generator sets. Idle Speed: 800-1,000 rpm (adjustable).
Emission Compliance: Variants exist from unregulated configurations to
full EU Stage V compliance, achieved via electronic control, refined
combustion, and integrated Diesel Oxidation Catalyst (DOC) / Diesel
Particulate Filter (DPF) systems. Management System: Mechanical fuel
system with mechanical governor on base models. Emission-compliant
models employ a full-authority Engine Control Unit (ECU).
The cylinder block is a rigid, single-piece casting manufactured from
high-strength gray iron. It features a closed-deck design, providing
maximum structural integrity around the cylinder bores and upper
cranksase area, which is essential for containing combustion pressures
and minimizing noise. The cylinder bores are precision-machined and
honed directly into the block material, a design that offers excellent
heat dissipation without separate liners.
The crankshaft is a forged or high-grade nodular cast iron component,
supported by four main bearings. This bearing count provides critical
stability for the three-cylinder crankshaft, effectively dampening
inherent vibrations. 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 with anodized ring grooves for wear resistance. IDI
pistons have a flat or shallow dish crown, while DI pistons feature a
specific re-entrant combustion bowl to generate controlled air swirl.
The piston ring pack comprises two chrome-plated compression rings and a
three-piece oil control ring.
A single-piece cast iron cylinder head is employed, secured to the block
with high-tensile studs and nuts. The head design accommodates one
intake and one exhaust valve per cylinder. Valve seat inserts are
manufactured from hardened, heat-resistant alloy to ensure longevity.
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 bolted to the cylinder
head. Valve clearance is set and maintained by a screw and locknut
adjustment on each rocker arm, requiring periodic manual inspection. The
cylinder head design differs fundamentally between IDI and DI types: IDI
heads incorporate a pre-combustion swirl chamber with a glow plug, while
DI heads position the injector nozzle centrally to spray directly into
the piston bowl.
The base engine configuration employs a mechanical pump-line-nozzle fuel
injection system. Core components include a mechanical lift pump, an
inline or distributor-type injection pump, high-pressure fuel lines, and
injectors. The injection pump is a jerk-pump design, driven by the
engine gear train. For Indirect Injection engines, the pump supplies
fuel to pintle-type nozzles that discharge into the pre-chamber.
Direct Injection engines use higher-pressure pumps supplying multi-hole
pintle nozzles for direct combustion chamber injection. A mechanical
centrifugal governor, integral to the injection pump, regulates engine
speed. On EU Stage V and other emission-compliant models, this system is
superseded by an electronically controlled, high-pressure common rail or
an advanced unit pump system, managed by an ECU for precise fuel timing
and dosage to meet emission limits.
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 screened pickup tube. Pressurized oil is routed
through a full-flow, spin-on cartridge oil filter. After filtration, oil
enters the main gallery in the block, supplying the crankshaft main and
connecting rod bearings, the camshaft bearings, and the valve gear via
internal passages and the hollow pushrods.
The system is designed for reliability with a simplified oil passage
network. The specified engine oil is API CD, CF, or for modern variants,
low-ash oils meeting API CJ-4 or ACEA E9 specifications to protect
after-treatment devices. Total oil capacity, including the filter, is
4.5 liters (4.8 US qt). The oil pan is a stamped steel or cast aluminum
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 controlled
by a wax-pellet type thermostat housed in the water outlet connection.
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, usually in a 30/70 to 50/50 ratio. Total cooling
system capacity for the engine side is 2.5 liters (2.6 US qt), excluding
the radiator, hose, and any external heat exchanger volume.
| Intake and Exhaust Systems |
Intake System: Consists of an air cleaner, intake manifold, and, on DI
models, intake ports engineered to generate swirl for improved air-fuel
mixing. Exhaust System: Comprises an exhaust manifold and downpipe. On
EU Stage V compliant models, this system integrates a Diesel Oxidation
Catalyst (DOC) and a Diesel Particulate Filter (DPF) in a single
canister, managed by the ECU which initiates active regeneration cycles
when required.
Electrical System: Operates on a 12V system. A 12V starter motor and a
12V alternator are standard. Indirect Injection models incorporate a
glow plug system for cold starting. An electric stop solenoid acts on
the injection pump rack. Stage V models feature a comprehensive sensor
suite (temperature, pressure, DPF differential pressure, NOx) and a
dedicated ECU.
Length (Front Face of Block to Flywheel Housing): 567.5-589 mm
(22.34-23.19 in)
Width (Overall): 432-442 mm (17.01-17.40 in).
Height (Overall, from sump to valve cover): 572 mm (22.52 in).
Dry Weight (with standard accessories): 135 kg (298 lb).
Engine Oil Change: Every 250 operating hours for standard models. For
Stage V models using low-ash oil, intervals may extend to 500 hours
(follow OEM specification). Oil Filter Replacement: Every oil change.
Fuel Filter Replacement: Every 500 operating hours. Water separator
should be drained daily or weekly. Air Cleaner Element Service: Clean or
replace based on restriction indicator; inspect frequently 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 at signs of wear or cracking.
After-Treatment Service (Stage V models): DPF ash cleaning is required
at extended intervals (e.g., 4,500 hours), dependent on fuel and oil
consumption.
Cylinder Head Nuts: Tighten in the specified crisscross sequence to a
final torque of 88-98 Nm (65-72 lb-ft).
Main Bearing Cap Bolts: 88-98 Nm (65-72 lb-ft).
Connecting Rod Cap Bolts: 49-59 Nm (36-44 lb-ft).
Flywheel to Crankshaft Bolts: 88-98 Nm (65-72 lb-ft).
Fuel Injector Holder: 59-69 Nm (44-51 lb-ft) for DI types.
Glow Plug: 15-20 Nm (11-15 lb-ft) for IDI types.
Oil Pan Drain Plug: 39-49 Nm (29-36 lb-ft).
Oil Filter Cartridge: Hand-tighten plus 3/4 turn after the gasket
contacts the base.
The Mitsubishi S3L2 engine is a prevalent and trusted power source in
the global market for compact construction and industrial equipment. Its
primary applications include: Compact Excavators: Caterpillar (CAT)
301.5, 301.6, 301.8; Volvo ECR28, ECR38; Pel-Job 0085SR, 010SR; Yanmar
VIO series mini-excavators. Generator Sets: Mobile and stationary diesel
generators in the 10-20 kVA power range.
Welding Equipment: Engine-driven welding generators. Material Handling:
Small telescopic handlers and compact forklifts. Agricultural Machinery:
Small tractors, power units for irrigation pumps, and post-hole diggers.
Pumping Equipment: Medium-capacity water transfer and dewatering pumps.
Compaction Equipment: Small ride-on rollers and plate compactors.
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