Yanmar 4-Stroke 20HP Marine Engine Parts

(6 products)

This page is dedicated to Yanmar 4‑Stroke 20HP outboard engines. Use it to find compatible parts and service guidance, including maintenance tips, common replacement items, and troubleshooting help. You can also browse our main Yanmar collection. Scroll to the bottom of the page to start browsing parts for this engine, and remember you can use the Filter & Sort controls on collection pages to narrow results by horsepower, year range, and part category/section.

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How to Identify Your 20HP Model

Locate the nameplate/serial plate on the transom clamp bracket or mounting bracket. It lists the full model code, serial number, and sometimes the manufacturing date.
Model code and suffixes typically indicate shaft length (S/L/XL), control type (tiller vs. remote), and regional spec. Match these details when selecting parts.
For 4‑Stroke models, note whether your unit uses EFI or a carburetor. Fuel and ignition parts can differ by system and year.
Verify propeller spline count and gear ratio when ordering propellers or gearcase components.

Engine Overview

20HP 4‑Stroke Platform

Feature	Description
Configuration	Compact inline 4‑stroke, typically twin‑cylinder; EFI or carbureted depending on year and region.
Common Models	20HP 4‑Stroke models with short/long shaft and tiller/remote variants (confirm via serial plate).
Advantages	Low noise and vibration, efficient fuel use, strong mid‑range torque, low maintenance compared with older 2‑Strokes.
Notes	Match parts to model code, serial range, shaft length, and control type. Cooling and fuel parts can differ by EFI/carb and production year.

Routine Maintenance & Service Parts

Intervals below are general guidelines for small 4‑Stroke outboards. Always follow the service schedule and procedures in your official owner’s/service manual.

Item	Interval*	Remarks	Parts Link
Engine oil & oil filter	First 20 hrs, then every 100 hrs or annually	Warm engine before draining; replace crush washer as needed.	Yanmar Oil Filters
Gear oil (lower unit)	Every 100 hrs or annually	Inspect magnets for metal; check for water intrusion (milky oil). Replace seals if needed.	Lower Unit Seal Kits
Spark plugs	Inspect every 100 hrs; replace as required	Verify heat range and gap for your specific model/year.	Spark Plugs
Fuel filter / water separator	Every 100 hrs or annually	Drain water and replace element more often with E10 fuel or storage use.	Yanmar Fuel Filters
Water pump impeller/kit	Every 2 seasons or 200 hrs (whichever comes first)	Replace sooner if weak tell‑tale or overheat alarms occur.	Water Pump Impeller Rebuild Kits
Anodes (internal & external)	Inspect every 50 hrs; replace when 50% consumed	Use the correct alloy for your waters (zinc, aluminum, or magnesium).	Anodes
Thermostat inspection	Check every 2–3 seasons	Replace if corroded or not opening at spec temperature.	Cooling System Parts

Frequently Used Parts Categories

Routine Service & Tune‑Up: Yanmar Service & Maintenance Kits
Cooling System: Water Pumps and Impeller Kits
Fuel System: Fuel Filters and Fuel Pumps
Ignition / Electrical: Spark Plugs and Starters
Corrosion Protection: Anodes
Propulsion & Gearcase: Propellers and Lower Unit Seal Kits
Accessories & Rigging: Boat Accessories

Common Symptoms & Quick Checks

Symptom	Check First	Related Parts
Weak tell‑tale stream or overheat alarm	Inspect intake screen for blockage; verify impeller condition; test thermostat operation.	Water pump impeller kit, pump housing, thermostat
Poor acceleration / power loss	Check prop damage/cavitation; replace clogged fuel filter; inspect plugs; verify throttle opens fully.	Propeller, fuel filter, spark plugs
Hard starting / rough idle	Use fresh fuel; inspect/replace spark plugs; check for air leaks; clean injectors or carb circuits as applicable.	Spark plugs, fuel filter, injector service or carburetor kit
Gearcase noise or metal in gear oil	Confirm correct oil level; look for water intrusion (milky oil); pressure test gearcase if seals suspected.	Lower unit seal kit, drain/fill gaskets, prop hardware

FAQs

Are parts interchangeable across different years or platforms?

Not always. Even within 20HP 4‑Stroke models, changes to ignition, fuel, or cooling systems occur by year and region. Always match the full model code, serial number, shaft length, and control type before ordering.

When should I replace the water pump impeller?

As a preventive measure, replace the impeller every two seasons or ~200 hours. Replace sooner if you notice a weak tell‑tale stream, overheat alarms, or after running dry/sandy water.

How often should I change lower unit gear oil?

Change every 100 hours or annually, and always after any impact or suspected water intrusion. Inspect the oil for metal debris and milky coloration.

What information do you need to confirm part compatibility?

Please provide the full model code, serial number, shaft length (S/L/XL), control type (tiller/remote), and any observed part numbers. A clear photo of the nameplate and the part needing replacement is very helpful.

Ready to find parts by horsepower, year, and model? Browse our main Yanmar collection and use the Filter & Sort controls to narrow your results.

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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.