Tohatsu · Outboard

Tohatsu MFS9.8

The MFS9.8 is Tohatsu’s light two-cylinder, 209 cc four-stroke portable — one of the most common dinghy and tender motors, and an auxiliary on small yachts. It weighs about 37 kg in its lightest form (manual start, short shaft) and comes with 15, 20 or 25 in shafts, tiller or remote control, manual or electric start. The MFS8 is the 8 hp version of the same engine. The B generation (2017) brought a restyled cowling with a better seal; the C generation (MFS8C / MFS9.9C) followed and is not covered here.

Manuals & documents
Wear parts & part numbers
Service intervals
Specifications
Good to know
Videos & how-tos
On the marketplace

Manuals & documents

The links go straight to Tohatsu. We host no manuals or drawings — the manufacturer’s copy is the current one.

Owner’s manual MFS6BZ / MFS8B / MFS9.8B (EU) Operation manual tohatsu.com · PDF · EN
Owner’s manual, German (EU B) Operation manual tohatsu.com · PDF · DE
Owner’s manual, French (EU B) Operation manual tohatsu.com · PDF · FR
Owner’s manual, Spanish (EU B) Operation manual tohatsu.com · PDF · ES
Owner’s manual MFS8B / MFS9.8B (US model) Operation manual tohatsu.com · PDF · EN
Owner’s manual MFS6A3Z / MFS8A3 / MFS9.8A3 (EU) Operation manual tohatsu.com · PDF · EN
Tohatsu owner’s manuals (all models and languages) Manual portal tohatsu.com · EN
Tohatsu online parts catalogue (accept the terms to open it) Parts catalogue tohatsu-partscatalog.aftama.com · EN
Tohatsu propeller selection chart Manual portal tohatsu.com · EN

Wear parts & part numbers

Part	OEM number	Also fits	Note
Raw water pump impeller	`3B2-65021-1`^2,3,4	Sierra `18-8920`¹	Also in Tohatsu’s official kit for the successor MFS8C/9.9C.
Water pump repair kit	`3B2-87322-2`^5,6replaces 3B2-87322-0replaces 3B2-87322-1	Sierra `18-3259`⁵	Impeller, liner, guide plate, gaskets and hardware.
Water pump gaskets	`3B2-65029-2` · `3B2-65018-2`^7,3	—	Guide plate gasket and pump case gasket.
Impeller drive key	`3B2-65022-0`^7,3	—
Service kit	`3V1-87500-0`^8,3	—	Tohatsu’s maintenance kit for MFS8/9.8 A3 and B; the contents differ between dealer listings.
Spark plug	`NGK DCPR6E`^9,4	—	Two per engine; Tohatsu number 9701-1-1103. Gap 0.8–0.9 mm.
Fuel filter (engine)	`369-02230-1`^7,3replaces 369-02230-0	—	In-line filter under the cowl.
Drain plug gasket	`3R3-07406-0`^7,3	—	Fit a new one at every oil change.
Gear oil plug gaskets	`332-60006-1`^7,3replaces 332-60006-0	—	Two per change (drain and level plug); never reuse.
Anode (lower unit)	`3V1-60217-0`^10,4	Martyr `CM3V1602170A`¹⁰	Trim tab anode on the gear case; also in Tohatsu’s kit for the C generation.
Timing belt	`3V1-10045-0`¹¹	—	Dealer job; one source only.
Propeller	`3B2B64517-1`^12,13	—	3-blade aluminium 8.9 × 8.5 in, standard on the short shaft; the long shaft comes with 8.5 × 7.5 in (3B2B64515-1).
High-thrust propeller (4-blade)	`3V1B64510-1`^12,14replaces 3V1B64510-0	—	4-blade 8.7 × 5 in for heavy tenders or pushing a yacht; a 7 in pitch (3V1B64514-1) sits between.
Propeller hardware kit	`3UB-87326-0`¹³	—	Thrust holder, washer, nut and split pin.

Numbers checked against the sources below on 12 October 2026. Always confirm against your serial number and exact type before ordering.

Service intervals

Task	Interval
Engine oil change	Every 100 h or every 6 months, first time after 20 h⁹
Gear oil change	Every 100 h or every 6 months, first time after 20 h⁹
Raw water impeller	Replace yearly (A3 and US B manuals); 2023 EU B manual: dealer check every 200 h or yearly^15,9
Spark plug	Check, clean and gap every 100 h or 6 months, first after 20 h; replace when worn¹⁶
Fuel filter	Check every 50 h or 3 months, first after 20 h; replace if it holds water or dirt⁹
Anode	Check every 50 h or 3 months; replace once about a third is gone¹⁵
Thermostat	Check every 100 h or 6 months (A3 / US B); every 200 h or yearly (2023 EU B)^16,9
Valve clearance	First at 20 h, then every 100 h or 6 months (A3 / US B); every 200 h or yearly (2023 EU B) — dealer job^16,9
Timing belt	Check every 100 h or 6 months (dealer)⁹
Carburettor	Strip, clean and adjust every 100 h or 6 months (dealer)¹⁶
Lubrication	Every 50 h or every 3 months, first time after 20 h⁹
Full service	Full inspection at 300 h, including a fuel pump strip-down¹⁵

Hours or months, whichever comes first. The A3 and US B manuals schedule more often than the 2023 EU B manual; where they differ, both are given.

Specifications

Cylinders	2, four-stroke⁹
Displacement	209 cc (55 × 44 mm)⁹
Power	7.2 kW (9.8 hp); MFS8: 5.9 kW (8 hp)⁹
Full-throttle range	5,000–6,000 rpm¹⁶
Idle speed	950 rpm (900 in gear)¹⁶
Cooling	Raw-water cooled with thermostat; exhaust through the propeller hub⁹
Engine oil capacity	approx. 0.8 l (27 US fl oz)⁹
Engine oil grade	SAE 10W-30 or 10W-40, API SH/SJ/SL; NMMA FC-W outboard oil recommended¹⁵
Gear oil capacity	approx. 0.32 l (10.8 US fl oz)¹⁷
Gear oil grade	API GL-5 SAE 80W-90 or Tohatsu gear oil¹⁷
Spark plug	NGK DCPR6E (2), gap 0.8–0.9 mm⁹
Valve clearance (cold)	Intake 0.13–0.17 mm, exhaust 0.18–0.22 mm⁹
Gearbox	F-N-R dog clutch, 2.08:1⁹
Shaft length	S 15 in, L 20 in, UL 25 in (transom 435 / 562 / 689 mm)¹⁵
Dry weight	37 kg (manual start, S) to 49 kg (electric start, power tilt, UL)⁹
Fuel	Unleaded petrol, RON 91 or higher (AKI 87); separate 12 l tank⁹
Alternator	12 V / 7 A (electric-start versions)⁹
Tightening torques	Oil drain bolt 24 N·m, gear oil plugs 4 N·m, spark plugs 18 N·m⁹
Propeller sizes	3-blade: 8.5 × 6.5 in (3B2B64513-1), 8.9 × 7 in (3B2B64514-1), 8.5 × 7.5 in (3B2B64515-1, standard L), 8.9 × 8.5 in (3B2B64517-1, standard S), 8.9 × 9.5 in (3B2B64519-1); 4-blade high thrust: 7 in (3V1B64514-1), 8.7 × 5 in (3V1B64510-1)^13,12
Years built	MFS9.8A from 2004, MFS9.8B from 2017^18,19

Good to know

Fit a new impeller every year even if the motor has hardly run — the rubber ages with time, not only with hours. While the lower unit is off, grease the driveshaft splines and the pump bolts.²⁰
Every start: the tell-tale must give a steady stream. If it weakens or stops, look at the water intake first, then at the impeller.¹⁵
After salt or brackish water, flush with fresh water: prop off, flushing attachment into the gear case water plug, intake taped over, 3–5 minutes idling in neutral.¹⁵
To carry it in the dinghy or a car, drain the fuel and lay it on its port side only, powerhead raised a little — otherwise oil runs where it should not.¹⁵
Change the gear oil in autumn so no condensation sits in the gear case over winter. Milky gear oil means water is getting past the seals.²⁰
Choose a prop that lets the motor reach 5,000–6,000 rpm at full throttle. For a heavy tender or pushing a yacht, the 4-blade high-thrust props are the ones.¹³

Videos & how-tos

Links to YouTube, nothing embedded. The maker’s own channel comes first; the rest are channels we found clear and correct for this model.

Changing the water pump impeller on the Tohatsu / Mercury 9.8 Video Umiox Fishing Japan · EN · 11 min
Impeller change on the MFS9.8B, step by step (German) Video clemensberlin · DE · 17 min
Engine oil and gear oil change on the Tohatsu 9.8 Video tc’s adventures · EN · 12 min
Removing and cleaning the carburettor on the Tohatsu 9.8 Video Umiox Fishing Japan · EN · 16 min

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Sources

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