3YM20
The Yanmar 3YM20 is a 0.854-litre naturally aspirated three-cylinder marine diesel rated 21 mhp (15.3 kW) at 3600 rpm. It is a freshwater-cooled sailboat and small-craft auxiliary in the YM series, sold with a KM2P-1 gear for shaft drive or with a saildrive.
The 3YM20 appeared with the 3YM30 in 2004 as the first engines of Yanmar's YM series, which succeeded the GM-series auxiliaries. It shares the 70 x 74 mm bore and stroke of the two-cylinder 2YM15, adding a third cylinder; like the rest of the series it is a vertical four-stroke with swirl pre-combustion chamber, in-line injection pump and freshwater cooling through a heat exchanger.
It is offered with the KM2P-1 mechanical cone-clutch reverse gear for shaft installations or with a saildrive (SD20 in earlier documentation, SD25 today). It is still listed by Yanmar, now with a 125 A alternator and EPA Tier 3 / RCD 2 / BSO II certification.
Specifications
Power
- Power
- 21 hp
- Power (kW)
- 15 kW
- Rated speed
- 3600 rpm
Engine
- Configuration
- inline 3
- Cylinders
- 3
- Displacement
- 0.854 L
- Aspiration
- naturally aspirated
- Weight
- 130 kg
- Fuel
- Diesel
- Mounting
- Inboard
Reviews
No independent reviews on file yet.
Sources
- 1. 3YM20 product page (Wayback capture Feb 2026) — Yanmar Marine International
- 2. 3YM20 datasheet DS_3YM20_A4_022021 — Yanmar Marine International
- 3. YM Series Operation Manual 0AYMM-M0002E (2025.02): 2YM15, 3YM20, 3YM30AE — Yanmar
- 4. YM Series Operation Manual 0AYMM-EN0023: 2YM15, 3YM20, 3YM30AE, 3YM30E, 3YM30 — Yanmar
- 5. YM Series Operation Manual P/N 0AYMM-G00200 (2009): 2YM15, 3YM20, 3YM30 — Yanmar Marine International (hosted by J/109 class)
- 6. Service Manual M9961-03E101 3YM30/3YM20/2YM15 (new edition March 2004, R1 April 2005) — Yanmar (hosted by J/109 class)
Specifications compiled from manufacturer sources.