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Yanmar 4-Stroke 15-30HP Marine Engine Parts

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This page is dedicated to Yanmar 4‑Stroke 15–30 HP marine diesel engines. Use it to find compatible parts and service information for popular YM‑series models, with maintenance tips, common replacement parts, and quick troubleshooting guidance. You can also browse the main Yanmar collection. Scroll to the bottom of the page to start browsing parts for this engine, and remember you can use the collection’s Filter & Sort controls to narrow results by horsepower, year range, and part category.

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How to Identify Your 15–30 HP Model

  • Nameplate locations: the engine model/serial plate is on the rocker arm (valve) cover; the marine gear or saildrive has its own identification plate. Record both.
  • Model codes: common engines in this range are 2YM15, 3YM20, and 3YM30. Drive options include KM2P‑1 marine gear or SD20 saildrive. Suffixes may indicate gearing or configuration.
  • Visual cues: 2YM15 is a 2‑cylinder; 3YM20/3YM30 are 3‑cylinders. All are fresh‑water cooled via heat exchanger with raw‑water (seawater) pump and flexible mounts.
  • Controls: YM engines use a single‑lever remote control for shift and throttle; ensure NEUTRAL interlock is present when starting.

Engine Overview

Yanmar 2YM15

Feature Description
Configuration 2‑cylinder, vertical water‑cooled 4‑stroke diesel; swirl pre‑combustion chamber; heat‑exchanger cooled; raw‑water impeller pump
Common Models 2YM15 with KM2P‑1 marine gear or SD20 saildrive
Advantages Compact footprint, simple service access, low fuel consumption
Notes Observe initial 50‑hour oil changes; confirm belt tension and raw‑water flow after launch

Yanmar 3YM20

Feature Description
Configuration 3‑cylinder, vertical water‑cooled 4‑stroke diesel; swirl pre‑combustion; heat‑exchanger cooled
Common Models 3YM20 with KM2P‑1 marine gear or SD20 saildrive
Advantages Smooth running, reliable charging output, good mid‑range torque
Notes Service intervals similar to 2YM15; drain/separate water from fuel regularly

Yanmar 3YM30

Feature Description
Configuration 3‑cylinder, vertical water‑cooled 4‑stroke diesel; swirl pre‑combustion; heat‑exchanger cooled
Common Models 3YM30 with KM2P‑1 marine gear or SD20 saildrive
Advantages Higher output in the 30‑HP class, well‑suited to auxiliary sailboats
Notes Watch seawater discharge volume; clean strainer and check impeller if flow decreases

Routine Maintenance & Service Parts

Intervals below are typical guidelines for YM‑series engines. Always follow your specific Yanmar service manual and local operating conditions.

Item Interval* Remarks Parts Link
Engine oil (diesel) Initial 50 hrs; then ~150 hrs or annually Change more often for heavy use; use correct API/viscosity for climate Yanmar Service & Maintenance Kits
Oil filter Initial 50 hrs; then ~250 hrs Replace with each second oil change unless manual specifies otherwise Yanmar Oil Filters
Fuel filter (engine) ~250 hrs or annually Drain any water; replace sooner if contamination is suspected Yanmar Fuel Filters
Fuel/water separator (pre‑filter, if equipped) Inspect/drain ~50 hrs; element as needed Bleed air after service; keep spare element and O‑rings aboard Fuel Filters
Raw‑water pump impeller Inspect each season; replace ~1000 hrs or 4 years (or sooner if flow weak) Carry a spare; replace cover gasket/O‑ring when serviced Impellers
Anodes (heat exchanger/drive) Inspect 100 hrs/seasonally; replace when 50% depleted Check bonding and zinc/aluminum type based on water chemistry Anodes
Alternator/drive belt Check tension 50 hrs; replace ~1000 hrs or 4 years Adjust to spec; avoid belt glaze/slip Belts
Air intake silencer/element Clean ~250 hrs; replace as needed Keep intake free of debris for best combustion Yanmar Air Filters
Marine gear (KM2P‑1) oil Initial 50 hrs; then ~150 hrs or annually Use specified gear oil; check level often Yanmar Parts
Saildrive (SD20) gear oil Initial 50 hrs; then ~100 hrs Inspect for water ingress; replace seals as needed Yanmar Parts
Thermostat & cooling hoses Inspect each season Overheating often traces to flow restriction or failed thermostat Hoses

Frequently Used Parts Categories

Common Symptoms & Quick Checks

Symptom Check First Related Parts
Weak water stream or overheat alarm Open seacock; clean intake strainer; inspect/replace raw‑water impeller; confirm belt tension Water pump impeller kit, cover gasket/O‑ring, thermostat, hoses
Poor acceleration or power loss Drain water from separator; replace fuel filter; verify clean air intake; check propeller load/fouling Fuel filter, pre‑filter/separator element, air filter
Hard starting or rough idle (cold) Battery state of charge; pre‑heat (glow) procedure; fuel quality/air in lines; valve lash due interval Battery/electrical items, fuel filter, bleed fittings, valve cover gasket (for adjustment)
Black smoke under load Air restriction or prop over‑pitched/dirty hull; injector service interval; check for overloading Air filter, gaskets, injector service parts
Gear noise or metal in drive oil Change gear oil; inspect seals for water ingress; verify alignment and shift cable adjustment Gear oil, seals, bearings (marine gear/saildrive)

FAQs

Are parts interchangeable between different years or platforms?

Many service items (filters, belts, impellers) are shared across YM models, but compatibility can change with drive type (KM2P‑1 vs SD20) and year updates. Confirm your engine model, serial number, and drive model before ordering.

When should the raw‑water impeller be replaced?

Inspect every season and replace at signs of wear or weak flow. Yanmar guidance is typically around 1000 hours or every four years, whichever comes first; many sailors replace more frequently based on usage and water quality.

How often should gear oil be changed?

For KM2P‑1 marine gear: initial 50 hours, then about every 150 hours or annually. For SD20 saildrive: initial 50 hours, then about every 100 hours. Always verify the correct oil specification for your drive.

What information helps confirm part compatibility?

Please provide the engine model and serial number (e.g., 2YM15, 3YM20, 3YM30), the drive model (KM2P‑1 or SD20), boat year, and any existing part numbers. Photos of the nameplate and the part you’re replacing are very helpful.

Ready to find the right parts for your Yanmar 4‑Stroke 15–30 HP engine? Browse the main collection and use Filter & Sort to refine by horsepower, year, and category.

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If you’re unsure about your model, send us a photo of the nameplate and the part you need and we’ll help verify compatibility.
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