Yanmar 6LY3 UTP Specifications
| Engine Model: Yanmar 6LY3 UTP |
| Engine Type: 4-stroke inline 6-cylinder turbocharged water-cooled diesel |
| Total Displacement: 354.7 cu.in (5.81 L) |
| Rated Engine Power: 380 Hp (279 kW) at 3300 rpm |
| Fuel System Type: Direct injection |
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The Yanmar 6LY3-UTP is a 5.8-liter, inline-six,
turbocharged and intercooled marine diesel engine produced from the
mid-2000s through the present. As part of the 6LY3 series, this power
unit introduced a 24-valve cylinder head and an electronic governor for
more precise fuel control and improved emissions compliance compared to
the earlier mechanical LY2 series.
The UTP designation indicates a specific power rating of 380 hp at 3,300
rpm, positioned below the higher-output 480 hp ETP variant while sharing
the same compact slim-block footprint. This design approach results in
lower mechanical stress on internal components, contributing to
reliability in light-duty commercial and pleasure craft applications.
The Yanmar 6LY3-UTP uses direct injection combustion with an electronic
hydraulic injection timer, a turbocharger, and a seawater-cooled
intercooler. The engine is compatible with Yanmar’s VC10 electronic
control system for drive-by-wire throttle and shift operation. Emissions
compliance includes US EPA Tier 2, EU RCD, BSO II, and IMO standards,
making the engine suitable for regulated markets worldwide. The 6LY3-UTP
is rated for light-duty commercial or pleasure craft duty cycles.
The Yanmar 6LY3-UTP is a four-stroke, vertical, water-cooled, inline-six
diesel engine with a total displacement of 5,813 cc (5.8 L / 354.7
cu.in). The bore and stroke dimensions are 106 mm (4.17 in) and 110 mm
(4.33 in), respectively, creating an oversquare configuration that
balances torque production with high-rpm power delivery for planing hull
applications. The valvetrain employs a dual overhead camshaft (DOHC)
design with four valves per cylinder - two intake and two exhaust - for
a total of 24 valves. This 24-valve configuration improves volumetric
efficiency compared to two-valve designs.
The combustion system uses direct injection with an electronic governor
and hydraulic injection timer. Induction is provided by a turbocharger
with a seawater-cooled intercooler (aftercooler) to reduce intake air
temperature and increase charge density.
The compression ratio is set at 16.7:1, a value selected to balance
cold-start performance with the elevated cylinder pressures of
turbocharged operation. Maximum output is 279 kW (380 hp) at 3,300 rpm.
Continuous rating is 239 kW (325 hp) at 3,198 rpm. The rated speed range
for pleasure craft applications is 3,000 to 3,300 rpm. Rotation viewed
from the flywheel side is counter-clockwise.
The cylinder block is constructed from cast iron, a material selected
for its exceptional rigidity, wear resistance, and ability to withstand
the high mechanical and thermal stresses of turbocharged diesel
combustion. The inline-six configuration incorporates seven main
bearings supporting a forged steel crankshaft. The crankshaft is
dynamically balanced and fully counterweighted to minimize vibration
across the operating range. The connecting rods are forged steel.
The 6LY3-UTP shares the compact slim-block footprint with the
higher-output 6LY3-ETP. This common block design provides a wide safety
margin at the UTP power level, resulting in lower stress on internal
components. The water jacket surrounds the cylinders for effective heat
transfer. Piston cooling is accomplished through oil jets mounted in the
crankcase, directing a continuous spray to the underside of each piston
crown. The block incorporates a deep-skirt design to maximize structural
stiffness.
The cylinder head is manufactured from cast iron or aluminum alloy
depending on the production version, matching thermal expansion
characteristics with the block. The dual overhead camshaft (DOHC)
arrangement positions the intake and exhaust camshafts within the head,
supported by multiple bearing journals. The camshafts are driven by a
timing gear train or chain depending on the specific design iteration.
Valves are arranged in a pent-roof combustion chamber configuration with
a narrow included valve angle to promote efficient flame propagation and
accommodate four valves per cylinder. Valve actuation is provided by
bucket tappets or roller rocker arms. Hydraulic lash adjusters maintain
zero valve clearance throughout the engine’s operating life, eliminating
the need for periodic valve adjustment.
The valve springs are of the double-coil type to ensure positive valve
seating under the elevated cylinder pressures of turbocharged operation.
The combustion chamber incorporates a re-entrant bowl design in the
piston crown, optimized for the direct injection system’s spray pattern.
The cylinder head gasket is a multi-layer steel (MLS) design, providing
reliable sealing under fluctuating thermal and mechanical loads.
The fuel system is a direct injection system utilizing an in-line
injection pump with an electronic governor and hydraulic injection
timer. The electronic governor provides precise fuel control across the
engine speed range, improving response, fuel efficiency, and emissions
compliance compared to mechanical governor systems. The hydraulic
injection timer adjusts injection timing based on engine speed and load
for optimal combustion.
The injection nozzles are of the multi-hole type designed for direct
injection into the piston bowl. A feed pump draws fuel from the
vessel-mounted tank through a water-separating primary filter and a
secondary fine filter. The system is compatible with Yanmar’s VC10
electronic control system, which provides drive-by-wire throttle and
shift operation as well as engine monitoring and diagnostics.
The lubrication system is a forced pressure circuit utilizing a
gear-type oil pump. The pump draws engine oil through a strainer screen
before directing it through a spin-on full-flow oil filter. A
water-cooled oil cooler is integrated into the lubrication circuit to
maintain stable oil temperature under sustained high-load operation.
The main oil gallery distributes pressurized oil to the crankshaft main
bearings, connecting rod bearings, camshaft bearings, and piston cooling
jets. The turbocharger bearing receives oil from a dedicated feed line.
The total engine oil capacity is 18.0 L (19.0 qt) including the filter.
Recommended oil is API class CD, CE, CF, or higher with SAE viscosity
grades of 15W-40 for most ambient temperatures.
The cooling system is a fresh water (closed) circuit with a heat
exchanger and seawater-cooled intercooler. A belt-driven centrifugal
fresh water pump circulates a mixture of water and ethylene glycol
antifreeze through the cylinder block, cylinder head, oil cooler,
turbocharger, and the tube stack of the heat exchanger.
The seawater pump is a flexible-impeller type, drawing raw water through
a through-hull fitting and strainer, then circulating it through the
shell side of the heat exchanger and the intercooler before discharging
with the exhaust gases. The thermostat is a wax-pellet type positioned
on the fresh water outlet, maintaining engine temperature within the
range of 80°C to 90°C (176°F to 194°F). An expansion tank allows for
coolant expansion.
| Intake and Exhaust Systems |
Intake System: The intake manifold is constructed from aluminum. The
turbocharger provides boost pressure calibrated to the engine’s power
output. The seawater-cooled intercooler (aftercooler) reduces intake air
temperature, increasing charge density and power output. The air intake
system includes a flame arrestor for marine safety compliance.
Exhaust System: The exhaust manifold is constructed from cast iron, with
the turbocharger mounted directly to the manifold outlet. The
water-injected exhaust elbow mixes seawater from the cooling system with
exhaust gases, cooling the exhaust to safe temperatures for rubber
exhaust hoses.
Electrical System: The electrical system operates on 12 volts. A 3.0 kW
electric starter motor provides cranking power. A 12V-80A alternator
provides charging current for the vessel’s battery banks. Glow plugs are
installed in the cylinder head for cold-start assistance, with glow
duration controlled automatically by the electronic control system.
Engine Control System: The 6LY3-UTP is compatible with Yanmar’s VC10
electronic control system, providing drive-by-wire throttle and shift
operation, engine synchronization for twin-engine installations, and
comprehensive monitoring of engine parameters including RPM, coolant
temperature, oil pressure, and fuel consumption.
The overall length, measured from the front pulley to the flywheel
housing face, is 1,300 mm (51.2 in). Width across the cylinder head and
turbocharger is 800 mm (31.5 in). Height from the bottom of the oil sump
to the top of the cylinder head cover is 900 mm (35.4 in). The dry
weight of the engine, inclusive of the turbocharger, intercooler, intake
and exhaust manifolds, starter, alternator, and flywheel but without
transmission or fluids, is 640 kg (1,411 lb). Rubber-type flexible
engine mounts are used to reduce vibration transmission to the vessel
hull.
The 6LY3-UTP requires structured maintenance aligned with marine service
intervals. The engine oil and filter must be replaced after the first 50
hours of operation (break-in), then every 250 operating hours or
annually, whichever comes first. The oil capacity is 18.0 L (19.0 qt).
The fuel filters (primary and secondary) require replacement every 250
operating hours.
The seawater pump impeller requires inspection every 100 hours and
replacement every 500 hours or as indicated by reduced seawater flow.
The heat exchanger and intercooler tube stacks should be removed and
cleaned every 500 operating hours. The valve clearance is maintained
automatically by hydraulic lash adjusters and requires no periodic
adjustment.
The fresh water coolant requires replacement every 500 operating hours
or 24 months. The anodes in the seawater cooling circuit and heat
exchanger must be inspected annually and replaced when 50% consumed. The
VC10 electronic control system requires no periodic maintenance but
should have software updates applied as recommended by Yanmar.
Cylinder Head Bolts: Stage one: 70 Nm (52 lb-ft).
Main Bearing Cap Bolts: 100 Nm (74 lb-ft).
Connecting Rod Bolts: 70 Nm (52 lb-ft).
Camshaft Bearing Caps: 25 to 30 Nm (18 to 22 lb-ft).
Flywheel Bolts: 140 to 150 Nm (103 to 111 lb-ft).
Crankshaft Pulley Bolt: 300 to 350 Nm (221 to 258 lb-ft).
Intake Manifold Bolts: 25 to 30 Nm (18 to 22 lb-ft).
Exhaust Manifold Nuts: 35 to 40 Nm (26 to 30 lb-ft).
Turbocharger Mounting Nuts: 45 to 50 Nm (33 to 37 lb-ft).
Injection Pump Mounting Nuts: 30 to 35 Nm (22 to 26 lb-ft).
Injector Holders: 80 to 90 Nm (59 to 66 lb-ft).
Oil Pan Bolts: 20 to 25 Nm (15 to 18 lb-ft).
Glow Plugs: 15 to 20 Nm (11 to 15 lb-ft).
The Yanmar 6LY3-UTP engine was deployed exclusively in marine
applications, with no automotive or industrial variants.
Powerboats (32 to 40 feet): The 6LY3-UTP was installed in planing
powerboats, including center console fishing vessels, express cruisers,
and sportfishing yachts. The engine’s 380 hp output provided speeds from
30 to 45 knots on appropriate hull designs. Applications included
vessels from manufacturers such as Grady-White, Pursuit, Regulator,
Albemarle, and Jupiter.
Downeast and Cruiser Yachts: The engine was used in semi-displacement
and planing cruiser yachts, including downeast-style boats from
manufacturers such as Sabre, Back Cove, and Eastern. The inline-six
smoothness and electronic controls contributed to the refined operation
expected in cruising applications.
Light Commercial Vessels: The engine was installed in pilot boats,
patrol vessels, and small workboats where the electronic governor and
continuous rating provided reliable propulsion for extended operating
hours.
KMH61A Gearbox Applications: The Yanmar KMH61A hydraulic multi-disc
clutch with 8-degree down angle was the standard transmission pairing,
used in vessels requiring a direct propeller shaft connection.
KMH61V V-Drive Applications: The KMH61V V-drive configuration was
offered for vessels where the engine must be mounted aft-facing to
provide a forward propeller shaft installation. This layout was common
in certain cruiser and sportfish designs with mid-engine placement.
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