Yanmar 4LHA DTP Specifications
| Engine Model: Yanmar 4LHA DTP |
| Engine Type: 4-stroke inline 4-cylinder turbocharged water-cooled diesel |
| Total Displacement: 211 cu.in (3.45 L) |
| Rated Engine Power: 200 Hp (147 kW) at 3300 rpm |
| Fuel System Type: Direct injection |
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The Yanmar 4LHA-DTP is a 3.5-liter,
inline-four, turbocharged and intercooled marine diesel engine produced
from the early 2000s through the 2010s. As an evolution of the 4LH
series, this power unit provides increased power output while
maintaining a similar physical footprint, making it a popular choice for
powerboats, light-duty commercial vessels, and repower applications.
The Yanmar 4LHA-DTP employs direct injection combustion with an in-line
fuel injection pump, a turbocharger, and a seawater-fed intercooler to
achieve a maximum output of 200 hp from its 3.5-liter displacement. The
engine is built on a cast iron cylinder block with replaceable wet-type
cylinder liners, a forged steel crankshaft, and a fresh water cooling
system with a separate seawater pump for the heat exchanger.
The engine is offered with multiple transmission options, including the
Yanmar KMH50A hydraulic gearbox and the ZF63A, as well as Bravo
sterndrive configurations designated DTZP. The 4LHA-DTP complies with EU
RCD 1, BSO II, and EMC emissions standards, reflecting its design for
environmentally regulated markets.
The Yanmar 4LHA-DTP is a four-stroke, vertical, water-cooled,
inline-four diesel engine with a total displacement of 3.455 L (3,455 cc
/ 211 cu.in). The bore and stroke dimensions are 100 mm (3.94 in) and
110 mm (4.33 in), respectively, creating an undersquare configuration
that emphasizes low-end torque production - a critical characteristic
for marine propulsion applications. The valvetrain employs an overhead
valve (OHV) design with two valves per cylinder for a total of eight
valves. The camshaft is positioned within the cylinder block and
actuates the valves through pushrods and rocker arms.
The combustion system uses direct injection with an in-line fuel
injection pump. Induction is provided by a turbocharger with a
seawater-fed intercooler to reduce intake air temperature and increase
charge density.
Maximum crankshaft output is 147 kW (200 hp) at 3,300 rpm according to
ISO 3046-1, or 140 kW (190 hp) at 3,300 rpm according to ISO 8665:2006.
The power difference reflects different measurement standards and
auxiliary load allowances. The rated engine speed is 3,300 rpm. Rotation
viewed from the stern (flywheel side) is counter-clockwise. The engine
speed range for continuous operation is from idle to the rated maximum.
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-four configuration incorporates five 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.
A distinguishing feature of the 4LHA-DTP is its use of replaceable
wet-type cylinder liners. These liners are pressed into the block and
sealed with rubber O-rings at the lower end, allowing direct contact
between coolant and the outer surface of the liners for superior heat
dissipation.
This design enables the engine to be rebuilt to original specifications
without machining the block casting. The water jacket surrounds the
cylinder liners completely, providing uniform cooling to the combustion
chamber region. 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, matching the thermal
expansion characteristics of the block to ensure consistent head gasket
sealing under the elevated cylinder pressures of turbocharged operation.
The overhead valve (OHV) arrangement positions the camshaft within the
block, with valve actuation provided by pushrods and rocker arms. The
rocker arms pivot on a rocker shaft mounted to the cylinder head and are
adjustable to set valve clearance.
Valves are arranged in-line along the cylinder head axis, with each
cylinder served by one intake valve and one exhaust valve. The direct
injection combustion chamber is formed primarily within the piston
crown, with the cylinder head providing a shallow recess to accommodate
the injector nozzle.
Valve seat inserts are pressed into the cylinder head and machined to
precise angles - usually 30 degrees for intake and 45 degrees for
exhaust - to ensure proper sealing under diesel combustion pressures.
The valve springs are of the single-coil type with heat-resistant wire.
The cylinder head gasket is a multi-layer steel (MLS) design, providing
reliable sealing between the cast iron head and cast iron block under
elevated turbocharged cylinder pressures.
The fuel system is a mechanical direct injection system utilizing an
in-line fuel injection pump mounted to the cylinder block and driven by
the timing gear train. Each cylinder has its own pump element (plunger
and barrel) delivering high-pressure fuel through steel lines to the
injection nozzles. A mechanical governor integrated into the injection
pump maintains engine speed under varying propeller loads.
The injection nozzles are of the multi-hole type designed for direct
injection into the piston bowl. A feed pump, integral to the injection
pump, draws fuel from the vessel-mounted tank through a water-separating
primary filter and a secondary fine filter. A manual primer lever allows
bleeding of air from the system after filter replacement.
The lubrication system is a forced pressure circuit utilizing a
gear-type oil pump mounted within the timing case. The pump draws engine
oil from a cast aluminum sump 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, rocker arm
assemblies, and the piston cooling jets. The turbocharger bearing
receives oil from a dedicated feed line. The total engine oil capacity
is 11.5 L (12.2 qt) including the filter. Recommended oil is API class
CD 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, protected by a separate seawater pump. 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. The total fresh water capacity is 8.0 L (8.5 qt). The
seawater pump impeller requires regular inspection and replacement.
| Intake and Exhaust Systems |
Intake System: The intake manifold is constructed from cast iron or
aluminum. The turbocharger is a fixed geometry or wastegate-controlled
unit providing boost pressure calibrated to the engine’s power output.
The seawater-fed 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.
The electrical system operates on 12 volts DC. A 2.5 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 a timer based on coolant temperature.
Timing Drive: The camshaft and injection pump are driven by a gear train
from the crankshaft. This gear drive system eliminates the need for
timing belt or chain replacements. Accessory drives for the fresh water
pump and alternator are belt-driven from the crankshaft pulley.
The 4LHA-DTP’s dimensions include the engine mounting configuration and
optional gearbox. The standard engine dimensions (bobtail, without
gearbox) are 850 mm (33.5 in) in length, 650 mm (25.6 in) in width, and
750 mm (29.5 in) in height. With the KMH50A gearbox, the overall
dimensions are 1,131 mm (44.5 in) length, 719 mm (28.3 in) width, and
811 mm (31.9 in) height.
The dry weight (bobtail) is 365 kg (805 lb). With the KMH50A gearbox,
the weight increases to 420 kg (926 lb). Rubber-type flexible engine
mounts are used to reduce vibration transmission to the vessel hull.
The 4LHA-DTP 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 200 operating hours or
annually, whichever comes first. The oil capacity is 11.5 L (12.2 qt).
The fuel filter requires replacement every 200 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 tube stack should be removed and cleaned every 500
operating hours or whenever seawater flow is reduced.
Valve clearance adjustment is required at intervals of 500 operating
hours, with cold clearances specified in the service manual. 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
intercooler (aftercooler) requires periodic cleaning of the seawater
passages.
Cylinder Head Bolts: 60 Nm (44 lb-ft).
Main Bearing Cap Bolts: 90 Nm (66 lb-ft).
Connecting Rod Bolts: 60 Nm (44 lb-ft).
Rocker Arm Shaft Bracket Bolts: 25 to 30 Nm (18 to 22 lb-ft).
Rocker Arm Adjustment Locknuts: 15 to 20 Nm (11 to 15 lb-ft).
Flywheel Bolts: 120 to 130 Nm (89 to 96 lb-ft).
Crankshaft Pulley Bolt: 250 to 300 Nm (184 to 221 lb-ft).
Intake Manifold Bolts: 25 to 30 Nm (18 to 22 lb-ft).
Exhaust Manifold Nuts: 30 to 35 Nm (22 to 26 lb-ft).
Turbocharger Mounting Nuts: 40 to 45 Nm (30 to 33 lb-ft).
Injection Pump Mounting Nuts: 25 to 30 Nm (18 to 22 lb-ft).
Injector Holders: 70 to 80 Nm (52 to 59 lb-ft).
Oil Pan Bolts: 15 to 20 Nm (11 to 15 lb-ft).
Glow Plugs: 15 to 20 Nm (11 to 15 lb-ft).
The Yanmar 4LHA-DTP engine was deployed exclusively in marine
applications, with no automotive or industrial variants.
Powerboats (22 to 30 feet): The 4LHA-DTP was a popular engine for
planing powerboats, including center console fishing boats, cuddy
cabins, and runabouts. The engine’s power-to-weight ratio enabled speeds
from 25 to 40 knots depending on hull design. Applications included
vessels from manufacturers such as Grady-White, Boston Whaler, Pursuit,
and EdgeWater.
Light Commercial Vessels: The engine was installed in small workboats,
pilot boats, and patrol vessels where reliable propulsion was required
for extended operating hours. The intercooled turbocharger provided the
torque necessary for pushing loads and maintaining speed in rough
conditions.
Sterndrive Configurations (DTZP): The DTZP variant was configured for
Bravo sterndrive applications, allowing the engine to be paired with
Mercruiser Bravo drives. This configuration was popular in larger
bowriders, deck boats, and performance runabouts where stern drive
outdrive access simplified maintenance.
Repower Applications: The 4LHA-DTP was used as a replacement engine for
older vessels originally powered by gasoline inboards or lower-output
diesels. The compact footprint allowed installation in engine
compartments originally designed for smaller displacement engines.
KMH50A Gearbox Applications: The Yanmar KMH50A hydraulic multi-disc
clutch with 8-degree down angle was used in vessels requiring a direct
propeller shaft connection. The ZF63A transmission, also an 8-degree
down angle hydraulic wet multi-disc clutch, was offered as an
alternative for installations with specific dimensional requirements.
Production of the 4LHA-DTP continued until the introduction of the 4LV
series and common-rail marine engines.
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