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Tohatsu M9.9C / M15C / M18D two-stroke (247 / 294 cc twin) service guide

Oil, gear oil, spark plugs and the service schedule for the Tohatsu M9.9C / M15C / M18D two-stroke (247 / 294 cc twin) (9.9 to 18 hp, two-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: Tohatsu 9.9C, 9.9CEF, 9.9CEP, 15C, 15CEF, 15CEP, 18D, 18DEF and 18DEP. 2 cylinders. 9.9 and 15: 247 cc, bore 55 x stroke 52 mm; 18: 294 cc, bore 60 x stroke 52 mm. 9.9 PS, wide open throttle 4,500 to 5,300 rpm; 15 PS, 4,750 to 5,500 rpm. Gasoline-engine oil mixture, 50 parts gasoline to 1 part oil, TCW-3 engine oil, forced water cooling (rubber impeller) with a thermostat and pressure release valve, magneto energized CD ignition, 12V 80W alternator, TK carburetor, dog clutch F-N-R, gear ratio 13:24. Premix, no oil injection.

Quick answers

What two-stroke oil does a Tohatsu M9.9C / M15C / M18D two-stroke use?
TCW-3 engine oil.
What is the fuel to oil ratio for a Tohatsu M9.9C / M15C / M18D two-stroke?
50 parts gasoline to 1 part oil. Running-in after engine parts are replaced: 20:1 for more than 10 hours.
What gear oil does a Tohatsu M9.9C / M15C / M18D two-stroke use, and how much?
Specified gear oil, GL5, SAE #80 to 90. Quantity: Approx. 370 cc.
What spark plug does a Tohatsu M9.9C / M15C / M18D two-stroke use?
NGK B7HS-10 or Champion L82, qty 2. Gap: 0.9 to 1.0 mm; repair, clean or replace when it is 1.2 mm or greater.
How often should a Tohatsu M9.9C / M15C / M18D two-stroke be serviced?
The factory schedule lists: Initial 10 hours; Every 50 hours or 6 months; Every 100 hours or 12 months; Every 200 hours or 12 months. In Hawaiʻi's salt water we do a full yearly service every 200 hours or 1 year, whichever comes first, and a new engine needs its first (break-in) service.
When should the water pump impeller be replaced on a Tohatsu M9.9C / M15C / M18D two-stroke?
The factory schedule says to replace it at 200 hours, and we follow that. In any case we never let it go longer than a year in Hawaiʻi's salt water.
What is the idle speed of a Tohatsu M9.9C / M15C / M18D two-stroke?
950 to 1000 rpm idling; 600 to 700 rpm with the clutch in.
What is the propeller nut torque on a Tohatsu M9.9C / M15C / M18D two-stroke?
Held by a propeller nut and split pin.

Maintenance specs

Two-stroke oilTCW-3 engine oil
Fuel to oil mix50 parts gasoline to 1 part oil. Running-in after engine parts are replaced: 20:1 for more than 10 hours
Gear oilSpecified gear oil, GL5, SAE #80 to 90
Gear oil quantityApprox. 370 cc
Gear oil upper and lower oil plugsThe drive shaft housing and gear case drawing lists the oil plug
Spark plugNGK B7HS-10 or Champion L82, qty 2
Spark plug gap0.9 to 1.0 mm; repair, clean or replace when it is 1.2 mm or greater
Spark plug torque2.4 to 2.6 kg-m (14 mm).
Idle speed950 to 1000 rpm idling; 600 to 700 rpm with the clutch in.
ThermostatStarts to open at 52 °C ± 2 °C, fully open at 65 °C ± 2 °C, valve lift more than 3 mm
AnodesEngine side anode, gear case anode and mounting bracket anode. Check for corrosion and wear when used; replace if necessary
PropellerHeld by a propeller nut and split pin

Service schedule

The factory maintenance intervals, with what is replaced and what is checked at each. Rows marked Hawaiʻi are our shop's yearly service for salt water use.

  1. Initial 10 hours

    Replace: gear case oil, gear case plug gaskets, propeller cotter pin

  2. Every 50 hours or 6 months

    Replace: gear case plug gaskets, propeller cotter pin

    Check: spark plugs, fuel filter, gear case oil

  3. Every 100 hours or 12 months

    Replace: gear case plug gaskets, propeller cotter pin

    Check: spark plugs, fuel filter, gear case oil, water pump impeller

  4. Every 200 hours or 12 months

    Replace: gear case oil, gear case plug gaskets, propeller cotter pin, water pump impeller

    Check: spark plugs, fuel filter

Source: Tohatsu 9.9 / 15 / 18 service manual. Specs can change by model year and serial number, so always confirm your exact model from the serial tag on the clamp bracket.

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