Yanmar 3YM20 Marine Engine Maintenance & Troubleshooting

Yanmar YM series diesel engines are the top choice for boat owners with small vessels, sailboats, and pleasure crafts. The integration of common rail fuel injection into lightweight applications makes these engines a source of clean and energy-efficient powering solution for propulsion systems. Despite the cutting-edge features, Yanmar engines require regular scheduled maintenance to achieve higher fuel efficiency and optimal performance. With a smart engine care regimen and on-time parts replacement with genuine items, vessel owners can enjoy an extended engine lifecycle, too.

In this blog post, we are offering everything you need to keep your Yanmar 3YM20 engines running in perfect condition for years. From a compatible spare parts list to troubleshooting tips, this article has all the information for vessel operators and technicians to take good care of Yanmar diesel engines.

Yanmar 3YM20 Marine Engine – An Overview

Yanmar 3YM20 is a robust diesel engine featuring a revolutionary three-cylinder block configuration. This 29HP engine offers a powerful 15.3 kW / 21 mhp rated output at 3600rpm and a displacement of 0.854 L / 52.1 cu. In. The in-line pump integration and common rail indirect injection combustion system make these engines ideal for achieving clean and noiseless operation even at higher torque—all in all, a fabulous powering solution for small pleasure crafts and sailboats. With a decent 2.4-2.7L oil capacity, the module is one of the best in high-output diesel engine technology. Stay safe with an eco-friendly model with RCD 2, EPA Tier 3, EPA Tier 3C, and BSO II EMC certification.

OEM Yanmar Spare Parts for 3YM20 Marine Engines

Timely maintenance is crucial for achieving optimal engine efficiency in Yanmar-powered vessels. The process also involves changing the worn-out and faulty parts with genuine items. Yanmar manufactures spare parts for its entire engine lineup. Choose Yanmar replacement parts by OEM part number to achieve the same output as delivered by the original components.

If you want to upgrade to a Yanmar 3YM20 diesel engine, it is highly recommended to keep the following spare parts handy. Regular maintenance and timely replacement of parts offer vessel safety and an extended engine lifecycle. Here is a list of original compatible spare parts for Yanmar 3YM20 engines.

Filters Components

Oil Filter (119305-35170)

Fuel Filter Element (104500-55710)

Air Filter Element (128270-12540 or 128170-12540 depending on version)

Cooling & Impellers

Impeller (128990-42200)

Yanmar Ready-Mixed Coolant (Pink) (COOLANT-PRO-5L)

Engine Components & Gaskets

Exhaust Mixing Elbow (L-type) (128370-13600)

Exhaust Manifold Gasket (104211-13201)

Cylinder Head Assembly (728170-11700)

Valve Stem Seal (124950-11340)

Packing, Pre-combustion Chamber (101204-11452)

Sensors & Electrical Systems

Oil Pressure Switch (124060-39452)

Electric Stop Solenoid (119653-77950)

Alternator & Belts

V-Belt for Alternator (A37.5) – (119831-42290)

Alternator (12V–125A) – (128990-77250)

Belt Cover Assembly – (128990-77460)

Alternator Drive Belt (119831-42290E)

Serpentine Belt (128790-77580)

Timing Belt (119771-00201)

Drive Belt for Seawater Pump (104511-78780)

Exhaust Components

Silencer Assembly – 128990-12500

Exhaust Mixing Elbow (L-type) – 128370-13600 (Elbow Assembly, mixing)

Gasket, Exhaust Manifold – 119717-13110

Engine Lubrication (Oil System)

Oil Filter Assembly (D68xL65) – 119305-35170

O-Ring, P15.0 – 119717-32060

Oil Inlet Pipe Assembly – 128890-35080

Oil Pressure Switch (hydraulic switch) – 114250-39450

Water & Cooling System

Fresh-Water Pump Assembly – 119540-42000

Seawater Pump V-Belt (M/19) – 104511-78780

Impeller Kit (Seawater Pump) – 128990-42570

Wear Kit (Seawater Pump) – 128990-42550

Water Cooler Assembly (Fresh-Water) – 128990-44900

Miscellaneous

Engine Stop Cable (104271-67550)

Oil Drain Connector (196311-92960)

Expansion Tank (fresh-water cooling) (OEM fit)

Flexible Engine Mounts (OEM fit)

B20 Control Panel (164100-30100)

Belt Cover Assembly – (128990-77460)

Air Intake Silencer Element – (128270-12540)

Yanmar Expansion Tank Parts for Fresh Water Cooler

Tank Assembly, Expansion – 748999-44260

Tank Assembly, Expansion – 148999-44050

Plug, M36×2 – 148620-01091

Cover – 153605-11720

Gasket, Tank Cover – 153605-11731

Gasket, 36×1.0 – 23414-360000

Bolt, M8×20 Plated – 26106-080202

Liner, Cylinder – 148960-44500

Filler Assembly – 126677-44600

Filler Assembly – 128623-44210

Gasket – 126650-44610

Bolt, M8×16 Plated – 26106-080162

Gauge, Level – 146613-44900

Bolt – 146613-4490C

O-Ring – 146613-4490D

O-Ring – 146613-4490E

Cock Assembly, 1/4 – 119620-49290

Washer, 12 – 22137-120000

Bolt, M12×60 Plated – 26116-120602

Bolt, M12×115 Plated – 26116-121152

Support – 148960-49370

Bolt, M12×25 Plated – 26116-120252

Bolt, M12×30 Plated – 26116-120302

Plug, Blind – 41649-000130

Plug, M36×1.5 – 127610-44900

Washer, Seal 36 – 22190-360002

Troubleshooting Tips for Yanmar 3YM20 Marine Engines

Problem 1 – The Engine does not start immediately after changing the fuel filter.

Probable reason and solution – Presence of air bubbles within the filter bracket. Bleed the filtration system to start the operations.

Things You Will Need

• 10mm/12mm spanners
• Nitrile gloves
• Rags
• Catch tray

Stepwise Guide

• Fill the primary (Racor) to the full level.
• Open the Fuel tank shutoff.
• Half-turn the bleed screw of the secondary filter of the engine.
• Work with the priming lever on the mechanical pump until the air bubbles escape from the fuel filter.
• Crack all the injector line nuts ½ turned at the injector. Give a burst for 10 seconds until the fuel spurts appear on each line. Now tighten the injector line nuts.
• Set the throttle to ~½. Preheating may be required if it is already fitted. Now start the system to hear a blip. The blip should be sufficient to remove the traces of remaining air bubbles.

Problem 2 – Wrong reading or dead Tachometer

Probable reason and solution – Find the W/stator signal at the alternator

Things You Will Need

• Wiring diagram/chart
• Contact cleaner
• Multimeter with (Hz) frequency

Stepwise Guide

• Locate the tack signal wire marked W/Y/P at the alternator
• Clean and tighten the spade/ring
• Run the engine to take the AC measurement
• Measure the AC on the tach lead to the engine ground.

Problem 3 – Engine Overheating at Higher RPM

Probable reason and solution – Faulty impeller replacement is required

Things You Will Need

• Screwdrivers
• Pliers
• New impeller
• Cover O-ring
• Belt
• Bucket

Stepwise Guide

• Open the seacock to check the seawater
• Clean the seawater strainer
• Pull the cover of the raw water pump
• Use a puller and pliers to remove the impeller
• Remove the hose connected to the heat exchanger inlet
• Clean the traces of chipped rubber particles on the exchanger
• If the vanes are missing, install the new ones after applying glycerine
• Remove the worn-out o-rings and replace them with new ones

Note: The Yanmar OEM impeller kit includes glycerine, O-rings, and replacement vanes.

Only genuine spare parts are good enough to keep your Yanmar-operated sailboats cruising without any glitches. Alfa Marine Spare Parts is your ultimate destination to purchase genuine Yanmar marine engines, accessories, and spares at affordable prices. Contact us today to procure OEM spare parts from the world's best marine engine brands – Cat, Cummins, Deutz, Detroit Diesel, Perkins, Scania, Wartsila, and others.