Yanmar 6LPA STP2 Specifications
| Engine Model: Yanmar 6LPA STP2 |
| Engine Type: 4-stroke inline 6-cylinder turbocharged water-cooled diesel |
| Total Displacement: 254 cu.in (4.16 L) |
| Rated Engine Power: 315 Hp (232 kW) at 3800 rpm |
| Fuel System Type: Direct injection |
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The Yanmar 6LPA-STP2 is a vertical, 6-cylinder,
4-stroke water-cooled marine diesel engine recognized for its compact
footprint and high power-to-weight ratio. The "STP2" designation
indicates a turbocharged and intercooled aspiration system with a
wastegate, combined with mechanical fuel injection. Unlike
electronically controlled common-rail engines of similar output, the
6LPA-STP2 employs a Bosch VE6 distributor-type injection pump with an
all-speed mechanical governor, simplifying troubleshooting and repair in
remote marine environments.
This engine is part of Yanmar's LP Series and is widely used in mid-size
cruising and sportfishing boats where a balance of power, weight, and
fuel efficiency is essential. A belt-driven overhead camshaft operates
24 valves, and an interference-type timing system requires scheduled
replacement at defined intervals. A freshwater cooling system with a
heat exchanger isolates the engine block from seawater corrosion.
The Yanmar 6LPA-STP2 operates on a four-stroke cycle with direct
injection. The inline six-cylinder configuration provides inherent
primary and secondary balance without requiring a balance shaft. The
wastegated turbocharger and seawater-cooled intercooler increase air
density before combustion, enabling high power output from a
displacement of 4.164 liters.
Engine Type: Vertical, 4-cycle, water-cooled diesel
Number of Cylinders: 6 (inline)
Displacement: 4.164 Liters (254 cu.in)
Bore x Stroke: 94 mm x 100 mm (3.70 in x 3.94 in)
Compression Ratio: 18.0:1
Aspiration: Turbocharged with wastegate and intercooler
Combustion System: Direct injection, 2-stage injection
Firing Order: 1-4-2-6-3-5
Rotation (viewed from flywheel): Counterclockwise
Maximum Output (Crankshaft): 232 kW (315 hp / 311 bhp) at 3800 RPM
Continuous Output (Crankshaft): 211 kW (286.4 hp) at 3682 RPM
Maximum Continuous Output (Marine): 191-211 kW (260-286 hp) at 3600 RPM
Governed Maximum Speed (no-load): 3900 RPM
Idle Speed: 700 ± 25 RPM
The cylinder block on the 6LPA-STP2 is a cast-iron monobloc design with
integral (parent-bore) cylinder bores. No replaceable cylinder liners
are used, as the precision-honed bores maintain surface finish for the
piston rings throughout the engine's service life. The deep-skirt
crankcase extends below the crankshaft centerline, providing rigidity
without excessive weight. Seven main bearings support the forged steel
crankshaft.
The oil pan is a pressed steel stamping sealed with a gasket. The front
of the block mounts a viscous damper to reduce torsional vibrations. A
front Power Take-Off (PTO) output is available for belt-driven auxiliary
equipment, with specific installation requirements including a maximum
pulley diameter of 170 mm and aluminum pulley construction.
The cylinder head is a single, cross-flow cast-iron casting spanning all
six cylinders. A single belt-driven overhead camshaft (OHC) operates the
valves through roller finger followers. This OHC design eliminates
pushrods, reducing reciprocating mass and improving valvetrain rigidity
at higher engine speeds. Four valves per cylinder - two intake, two
exhaust - optimize volumetric efficiency and permit central placement of
the fuel injector.
Valves per Cylinder: 4 (2 intake, 2 exhaust)
Valve Configuration: Overhead camshaft (OHC), belt-driven, roller finger
followers
Valve Clearance (Cold): 0.20 mm (0.008 in) for both intake and exhaust
Valve Adjustment Interval: 400 operating hours
Valve Seat Inserts: Induction-hardened steel
The cylinder head gasket is a multi-layer steel (MLS) design. The head
is secured using a torque-to-yield (TTY) procedure requiring angle
tightening. Valve bridges are installed between the camshaft lobes and
valve stems to actuate pairs of valves simultaneously.
The Yanmar 6LPA-STP2 employs a mechanical direct injection fuel system
without electronic controls. A Bosch VE6 distributor-type injection pump
is gear-driven from the engine timing gear case. This pump integrates an
all-speed mechanical governor that maintains stable speed under varying
loads, a critical feature for marine propulsion.
Injection Pump Type: Bosch VE6 distributor type, mechanical.
Injector Type: Mechanical, multi-hole.
Injection Pressure: 21.6 MPa (216 bar / 3130 psi).
Injection Timing: Adjustable via match marks on pump and timing gear
case.
Fuel Lift Pump: Mechanical diaphragm type.
Fuel Filters: Spin-on primary filter with integrated water separator;
secondary element on injection pump.
Fuel Consumption at Maximum Output: 35.0 L per hour (9.25 gal per hour).
Fuel Grade: Diesel meeting EN 590 or ASTM D975 No. 2-D.
The fuel system includes a manual hand-primer (bleed pump) on the filter
head for bleeding air after filter changes. A fuel cooler is installed
in the return line to prevent overheating of the fuel in tropical
conditions.
The lubrication system is a forced-feed, full-flow pressure system. A
trochoid-type oil pump, driven from the crankshaft, draws oil through a
suction strainer inside the oil pan. The oil passes through a full-flow
spin-on filter and then through a water-cooled oil cooler mounted on the
cylinder block.
Lubrication Type: Forced feed, full-flow filtration
Oil Pump Type: Trochoid
Oil Capacity (including filter): 12.0 Liters (12.7 U.S. quarts)
Oil Pressure (idle, hot): Minimum 1.0 bar (14.5 psi)
Oil Pressure (rated speed, hot): 3.0-4.5 bar (43-65 psi)
Oil Filter: Spin-on, full-flow cartridge type
Oil Cooler: Water-cooled, tube type
Oil Grade: API CF or higher, SAE 15W-40 (std) or SAE 10W-30 (cold
climates)
Oil Change Interval: 250 hours or 1 year
The cooling system is a dual-circuit design: a freshwater (closed-loop)
circuit cools the engine block and cylinder head, while a seawater
circuit removes heat through a heat exchanger and intercooler. An
engine-driven, belt-operated centrifugal pump circulates freshwater
through the cylinder block, cylinder head, turbocharger bearing housing,
and then through a tube-and-shell heat exchanger. A rubber impeller-type
seawater pump supplies raw water to the heat exchanger and the
seawater-cooled intercooler (charge air cooler).
Cooling System Type: Fresh water cooling with heat exchanger (Indirect).
Water Pump (Freshwater): Belt-driven, centrifugal.
Water Pump (Seawater): Crankshaft-driven, rubber impeller type.
Coolant Capacity (engine block only): 12.0 Liters (12.7 U.S. quarts).
Thermostat Opening Temperature: 71°C (160°F).
Thermostat Fully Open: 85°C (185°F).
Coolant Type: Ethylene glycol-based antifreeze with anti-corrosion
additives.
Zinc Anodes: Installed in heat exchanger and intercooler to prevent
galvanic corrosion; require periodic replacement.
The 6LPA-STP2 uses a 12-volt marine-rated electrical system. A
high-output alternator is standard.
System Voltage: 12 V DC (negative ground).
Alternator Output: 80 A.
Starter Motor: 12 V, 2.5 kW (3.4 hp).
Glow Plug System: Operated by key-switch preheat; sheathed ceramic type.
Air Intake and Turbocharging: Air enters through a dry-type paper
element air cleaner and passes through the turbocharger compressor. The
6LPA-STP2 uses a wastegated turbocharger, which diverts excess exhaust
gas at higher RPM to limit boost pressure and prevent mechanical
over-speed. Compressed air then passes through a seawater-cooled
intercooler (charge air cooler) to reduce intake air temperature before
entering the intake manifold. Turbocharger Type: Wastegated, fixed
geometry. Intercooler Type: Seawater-cooled, heat exchanger. Maximum
Boost Pressure: 1.5 bar absolute (7-8 psi gauge).
Exhaust System: A cast-iron dry exhaust manifold routes exhaust gases to
a water-injected mixing elbow. Seawater from the cooling system mixes
with the exhaust at the elbow, cooling the gases before they exit
through a reinforced rubber hose. Exhaust Pipe Diameter (dry section):
102 mm (4.0 in). Exhaust Type: Wet exhaust.
Dry Weight (Engine only): 408 kg (900 lbs)
Length (with KMH50A gearbox): 1,220 mm (48.0 in)
Width (with standard gear): 666-862 mm (26.2-33.9 in) depending on
exhaust configuration
Height: 739-784 mm (29.1-30.9 in)
Total Weight with KMH50A Gear: 450 kg (992 lbs)
Engine Oil and Filter Change: 250 hours or 12 months
Fuel Filter Primary (water separator): 250 hours; drain water weekly
Fuel Filter Secondary: 500 hours
Seawater Pump Impeller Inspection: 200 hours
Seawater Pump Impeller Replacement: 400 hours or at signs of cracking
Valve Clearance Adjustment: 400 hours
Anode Replacement (heat exchanger / intercooler): 250 hours or 6 months
Heat Exchanger Cleaning (seawater side): 2 years or 800 hours
Coolant Replacement: 2 years
Engine Mount Inspection: 400 hours
Timing Belt Replacement: 1,250 hours or 5 years
Injection Pump Timing Check: 1,000 hours (dealer service)
Injector Nozzle Replacement: 2,000 hours
Cylinder Head Bolts, Stage 1: 30 Nm (22 lb-ft)
Cylinder Head Bolts, Stage 2: 60 Nm (44 lb-ft) + 90 degrees
Connecting Rod Bolts: 30 Nm (22 lb-ft) + 70 degrees
Main Bearing Cap Bolts: 60 Nm (44 lb-ft) + 70 degrees
Flywheel Bolts: 65 Nm (48 lb-ft)
Crankshaft Pulley Bolt: 135 Nm (100 lb-ft)
Camshaft Timing Gear Nut: 55 Nm (41 lb-ft)
Injection Pump Set Nut: 103 Nm (76 lb-ft)
Injection Pump Mounting Nuts: 18 Nm (13.4 lb-ft)
Injection Pump Stay Bolts (to block): 69 Nm (51 lb-ft)
Injector Hold-Down Clamp Bolt: 25 Nm (18 lb-ft)
High-Pressure Fuel Line Nuts: 25 Nm (18 lb-ft)
Rocker Shaft Bracket Bolts: 25 Nm (18 lb-ft)
Valve Cover Bolts: 10 Nm (89 lb-in)
Oil Pan Bolts: 12 Nm (9 lb-ft)
Exhaust Manifold Bolts: 45 Nm (33 lb-ft)
Turbocharger Mounting Nuts: 45 Nm (33 lb-ft)
Intercooler Mounting Bolts: 25 Nm (18 lb-ft)
Starter Motor Mounting Bolts: 40 Nm (30 lb-ft)
Alternator Pivot Bolt: 25 Nm (18 lb-ft)
Glow Plug: 12 Nm (9 lb-ft)
Viscous Damper Bolts (to crankshaft pulley): 37 Nm (27 lb-ft)
The Yanmar 6LPA-STP2 is a marine propulsion engine and is not used in
land vehicles.
Sportfishing Boats (Express and Walkaround): Rampage 30 Express,
Grady-White Marlin, Pursuit 3070, and Boston Whaler Conquest models.
Mid-Size Cruisers (35 to 45 feet / 10.5 to 13.5 meters): Silverton,
Cruisers Yachts, and Regal models requiring single or twin
installations.
Downeast Boats: Semi-displacement hulls including Duffy, Ellis, and
Holland designs.
Pilothouse Motor Yachts: Cruising vessels from manufacturers such as
Parker, Steiger, and C-Dory.
Patrol and Law Enforcement Vessels: Small to mid-size patrol boats
requiring speeds up to 30 knots.
Water Taxis and Small Passenger Ferries: Commercial vessels operating in
high-speed planing configurations.
Rigid Inflatable Boats (RIBs): Large RIBs and RHIBs for military or
commercial use.
Catamarans: Power catamarans with one engine per hull in the 35-45 foot
range.
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