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Tohatsu M40D / M50D two-stroke (697 cc three-cylinder) service guide

Oil, gear oil, spark plugs and the service schedule for the Tohatsu M40D / M50D two-stroke (697 cc three-cylinder) (40 to 50 hp, two-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: Tohatsu M40D and M50D in M, EFO, EPO and EPTO versions. 3 cylinders, 697 cc (42.53 cu in), bore 68 x stroke 64 mm, three carburetors, firing order 1-2-3. M40D 29.82 kW (40 ps) at 5,000 rpm, full speed range 4,500 to 5,500 rpm; M50D 37.28 kW (50 ps) at 5,500 rpm, full speed range 5,000 to 5,700 rpm. Pressurized cooling by rubber impeller with a thermostat and pressure relief valve, pointless CD ignition magneto, dog clutch F-N-R, gear ratio 13:24, 22.7 L fuel tank. EFO, EPO and EPTO are auto mixing (oil injection) with a 2 liter integral oil tank. EPTO has power trim and tilt.

Quick answers

What two-stroke oil does a Tohatsu M40D / M50D two-stroke use?
Tohatsu 2-cycle Engine oil: SUPER GOLD. Oil tank 2 liters (0.53 gals); the low oil warning comes on at 0.4 liters (0.85 pt) or less.
What is the fuel to oil ratio for a Tohatsu M40D / M50D two-stroke?
Auto mixing models (EFO, EPO, EPTO): 50:1 to 120:1, set by the oil pump. When starting a new auto mixing outboard, add oil at 50:1 in the fuel tank as well as the oil in the oil tank.
What gear oil does a Tohatsu M40D / M50D two-stroke use, and how much?
Tohatsu gear oil. Quantity: Approx. 500 cc (1.06 pt). Fill through the lower plug hole until oil overflows from the upper plug hole; install the upper plug first, then the lower plug.
What spark plug does a Tohatsu M40D / M50D two-stroke use?
M40D: NGK B7HS-10 or Champion L82C. M50D: NGK B8HS-10 or Champion L78C. Qty 3. Gap: 1 mm (0.9 to 1.0 mm, 0.0354 to 0.0397 in); repair limit 1.2 mm (0.0472 in) or greater. Replace if electrode wear is extreme.
How often should a Tohatsu M40D / M50D two-stroke be serviced?
The factory schedule lists: Initial 10 hours or 2 weeks; Initial 30 hours or 1 month; Every 50 hours or 3 months; Every 100 hours or 6 months; Every 200 hours or once a year. 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 M40D / M50D two-stroke?
The factory schedule says to inspect it at 100 hours and 200 hours. In Hawaiʻi's warm salt water we replace it every 200 hours or 1 year, whichever comes first, because a worn impeller is the most common cause of overheating.
What is the idle speed of a Tohatsu M40D / M50D two-stroke?
Trolling speed 650 to 700 rpm; idling speed 850 to 900 rpm. Adjust with the air silencer cover installed.
What is the propeller nut torque on a Tohatsu M40D / M50D two-stroke?
29.4 to 39.2 N·m (3.0 to 4.0 kg-m, 21.69 to 28.92 lb-ft).

Maintenance specs

Two-stroke oilTohatsu 2-cycle Engine oil: SUPER GOLD. Oil tank 2 liters (0.53 gals); the low oil warning comes on at 0.4 liters (0.85 pt) or less
Fuel to oil mixAuto mixing models (EFO, EPO, EPTO): 50:1 to 120:1, set by the oil pump. When starting a new auto mixing outboard, add oil at 50:1 in the fuel tank as well as the oil in the oil tank
Gear oilTohatsu gear oil
Gear oil quantityApprox. 500 cc (1.06 pt). Fill through the lower plug hole until oil overflows from the upper plug hole; install the upper plug first, then the lower plug
Gear oil upper and lower oil plugs2 plugs (upper and lower oil plugs).
Spark plugM40D: NGK B7HS-10 or Champion L82C. M50D: NGK B8HS-10 or Champion L78C. Qty 3
Spark plug gap1 mm (0.9 to 1.0 mm, 0.0354 to 0.0397 in); repair limit 1.2 mm (0.0472 in) or greater. Replace if electrode wear is extreme
Spark plug torque24.5 to 29.4 N·m (2.5 to 3.0 kg-m, 18.08 to 21.69 lb-ft)
Idle speedTrolling speed 650 to 700 rpm; idling speed 850 to 900 rpm. Adjust with the air silencer cover installed
ThermostatStarts to open at 60 °C; opens fully at 70 °C
Fuel pipes and oil check valveFuel pipes must be replaced every two years. Change the oil mixing check valve every two years
AnodesTrim tab, cylinder head, and power trim and tilt anodes. Check for corrosion and wear every time before use; replace if worn by 1/3 or more; change the anodes every year
Propeller nut29.4 to 39.2 N·m (3.0 to 4.0 kg-m, 21.69 to 28.92 lb-ft)
Power trim and tilt fluid (EPTO)Automatic transmission fluid, NIHON SEKIYU ATF DEXRON, 550 cc. The oil level should reach the oil plug hole with the engine tilted up and the piston rods fully extended. PT/T oil plug 2.94 to 4.9 N·m (0.3 to 0.5 kg-m)

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 or 2 weeks

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

    Check: spark plugs, fuel filter

  2. Initial 30 hours or 1 month

    Replace: gear case oil, gear case plug gaskets

    Check: spark plugs

  3. Every 50 hours or 3 months

    Replace: gear case plug gaskets, propeller cotter pin

  4. Every 100 hours or 6 months

    Replace: gear case plug gaskets, propeller cotter pin

    Check: water pump impeller, thermostat, anodes

  5. Every 200 hours or once a year

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

    Check: thermostat, anodes

We replace the water pump impeller at every service from 200 hours up, which can be sooner than the factory schedule, because of Hawaiʻi’s warm salt water.

Source: Tohatsu M40D/M50D service manual, MAR 1991. 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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