Tohatsu 4-Stroke 4-5HP Outboard Marine Engine Parts

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This page is dedicated to Tohatsu 4-Stroke 4–5HP outboard engines. Use it to find compatible parts and practical service information. Below you’ll find maintenance tips, common replacement parts, and troubleshooting guidance. You can also browse our main Tohatsu collection at any time. Scroll to the bottom of the page to start browsing parts for this engine, and remember you can use the “Filter & Sort” controls on the collection page to narrow results by horsepower, year range, and part category.

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How to Identify Your 4–5HP Model

Find the nameplate/serial label on the transom bracket or swivel bracket. It lists the model (e.g., MFS4 or MFS5) and serial number.
Model code suffixes indicate shaft length and options: S/L for short/long shaft, and E for electric start where applicable.
These portable 4–5HP engines are 4‑stroke and carbureted. Confirm you are not looking at a 2‑stroke legacy model, as parts differ.
Check the cowling decal and carburetor style; 4‑stroke MFS4/MFS5 share many service parts with the MFS6 platform, but verify by serial.

Platform Overview

Tohatsu MFS4/MFS5 Portable 4‑Stroke

Feature	Description
Configuration	Single‑cylinder, carbureted 4‑stroke, CDI ignition, manual or optional electric start
Common Models	MFS4, MFS5 (S/L shaft variants); many service parts overlap with MFS6
Advantages	Lightweight, fuel‑efficient, simple maintenance, reliable low‑speed torque for trolling and dinghy duty
Notes	Carbureted models are sensitive to stale fuel—keep filters clean and use fresh fuel. Water pump service is key for cooling performance.

Routine Maintenance & Service Parts

Intervals below are general guidelines for small portable 4‑stroke outboards. Always follow the official service manual for your exact model and operating conditions.

Item	Interval*	Remarks	Parts Link
Engine oil (and filter/screen)	Initial 20 hrs; then every 100 hrs or annually	Most 4–6HP models use a strainer rather than a spin‑on filter; change oil more often in harsh use.	Tohatsu Outboard Parts
Gear oil (lower unit)	Every 100 hrs or annually	Inspect for water intrusion and metal on the drain plug magnet; replace seals if contamination is found.	Tohatsu Lower Unit Seal Kits
Spark plugs	Inspect every 100 hrs; replace as needed	Set to the specified gap; fouling often indicates rich idle or stale fuel.	Spark Plugs
Fuel filter / inline strainer	Every 100 hrs or annually	Replace or clean more often when using portable tanks or if ethanol fuel is stored.	Fuel Filters
Water pump impeller / kit	Every 2–3 seasons or 200 hrs	Critical for cooling; replace sooner if weak tell‑tale or after sand/silt operation.	Tohatsu Water Pump Repair Kits
Anodes (internal & external)	Inspect every 50 hrs; replace when 50% depleted	Essential for corrosion protection, especially in brackish/salt water.	Anodes

Frequently Used Parts Categories

Routine Service — Service & Maintenance Kits
Cooling System — Tohatsu Water Pump Repair Kits
Fuel System — Fuel Filters
Carburetion — Carburetors
Ignition — Spark Plugs
Lower Unit — Tohatsu Lower Unit Seal Kits
Corrosion Protection — Anodes

Common Symptoms & Quick Checks

Symptom	Check First	Related Parts
Weak tell‑tale stream or overheat alarm	Inspect intake screen for debris; verify impeller condition; check thermostat operation.	Water pump kit, impeller, thermostat
Poor acceleration or power loss	Confirm fresh fuel and open tank vent; check fuel filter/strainer and carb jets; inspect spark plug.	Fuel filter, carburetor kit, spark plug
Hard starting or rough idle	Verify choke/enrichment function; drain old fuel; clean idle circuit; check for air leaks on fuel line.	Carburetor components, fuel connector/line, spark plug
Gearcase noise or metal in gear oil	Inspect gear oil level/condition; check for water intrusion; evaluate prop shaft seal area.	Lower unit seal kit, gear oil (service)
Low‑oil warning or engine stops when tilted	Confirm crankcase oil level and correct engine trim angle; avoid overfilling.	Engine oil service, breather inspection

FAQs

Are parts interchangeable between MFS4, MFS5, and MFS6?

Many routine service parts overlap across these portable platforms, but jetting, gearing, and certain gaskets can differ by model, year, and shaft length. Verify by model and serial number before ordering.

When should I replace the water pump impeller?

As a rule of thumb, replace every 2–3 seasons or ~200 hours, and sooner after sandy/silty use or any overheat event.

How often should I change the lower unit gear oil?

Every 100 hours or annually. If you find milky oil or metal particles, service seals and re‑inspect after short use.

What information helps confirm part compatibility?

Provide the complete model code, serial number, shaft length (S/L), and any options (manual vs. electric start). Photos of the nameplate and the old part are very helpful.

Ready to find parts by horsepower and model? Browse our main Tohatsu collection and use the filters to narrow by engine family 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.