HawaiiOutboard Repair
(808) 824-4380 Request service
MenuClose

Tohatsu MFS40A / MFS50A (3 cylinder EFI four-stroke) service guide

Oil, gear oil, spark plugs and the service schedule for the Tohatsu MFS40A / MFS50A (3 cylinder EFI four-stroke) (40 to 50 hp, four-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: MFS40A ET (remote control and multi tiller handle) and MFS50A ET / EG (multi tiller handle); S, L and UL transoms; 3 cylinder SOHC, 866 cm³ (52.8 cu in), electronic fuel injection.

Quick answers

How much oil does a Tohatsu MFS40A / MFS50A take?
2.4 L (2.5 US qt) with filter; 2.2 L (2.3 US qt) without filter. Dipstick lower limit 1.9 L (2.0 US qt) with filter, 1.7 L (1.8 US qt) without.
What engine oil does a Tohatsu MFS40A / MFS50A use?
4 stroke engine oil, API SH, SJ or SL, SAE 10W-30 or 10W-40.
What gear oil does a Tohatsu MFS40A / MFS50A use, and how much?
Hypoid gear oil, API GL-5, SAE #80-90. Quantity: 500 cm³ (16.9 fl oz; 0.53 US qt). Fill through the lower plug hole with the motor vertical.
What spark plug does a Tohatsu MFS40A / MFS50A use?
NGK DCPR6E. Gap: 0.8 to 0.9 mm (0.032 to 0.035 in); limit 1.2 mm (0.047 in).
How often should a Tohatsu MFS40A / MFS50A be serviced?
The factory schedule lists: First 20 hours or 1 month; Every 50 hours or 3 months; Every 100 hours or 6 months; Every 200 hours or 1 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 MFS40A / MFS50A?
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 MFS40A / MFS50A?
850 ± 30 r/min after 5 minute warm-up.
What is the propeller nut torque on a Tohatsu MFS40A / MFS50A?
35 N·m (26 lb·ft) [3.5 kgf·m]; new split pin.

Maintenance specs

Engine oil4 stroke engine oil, API SH, SJ or SL, SAE 10W-30 or 10W-40
Engine oil quantity2.4 L (2.5 US qt) with filter; 2.2 L (2.3 US qt) without filter. Dipstick lower limit 1.9 L (2.0 US qt) with filter, 1.7 L (1.8 US qt) without
Oil filter18 N·m (13 lb·ft) [1.8 kgf·m] with filter wrench P/N 3AC-99090-0; Oil filter (bolt) M20 x 1.5: 30 N·m (22 lb·ft) [3 kgf·m]
Engine oil drain bolt (M14 x 1.5)24 N·m (18 lb·ft) [2.4 kgf·m]; oil the washer
Gear oilHypoid gear oil, API GL-5, SAE #80-90
Gear oil quantity500 cm³ (16.9 fl oz; 0.53 US qt). Fill through the lower plug hole with the motor vertical
Gear case leak test0.069 MPa (10 psi) [0.7 kgf/cm²], oil drained, held 10 seconds; do not go over
Spark plugNGK DCPR6E
Spark plug gap0.8 to 0.9 mm (0.032 to 0.035 in); limit 1.2 mm (0.047 in)
Spark plug torque18 N·m (13 lb·ft) [1.8 kgf·m]
Idle speed850 ± 30 r/min after 5 minute warm-up.
ThermostatStarts to open 60 °C ± 1.5 °C (140 ± 3 °F); fully open 75 °C (167 °F); lift 3.0 mm (0.12 in) or more
Cooling water pressure (reference)850 r/min 3.0 kPa (0.4 psi); 1500 r/min 13.6 kPa (1.9 psi); 3000 r/min 27.3 kPa (3.9 psi); 5000 r/min 41.3 kPa (6 psi), at the fuel cooler check port
AnodesEngine anode screw M5: 2 N·m (1.4 lb·ft); anode plug M16: 18 N·m (13 lb·ft). Replace when worn to 2/3 of new size.
Propeller nut35 N·m (26 lb·ft) [3.5 kgf·m]; new split pin
Power trim and tilt fluidATF DEXRON III; full when fluid spills at the cap hole, motor tilted fully up; capacity 325 cm³ (11.0 fl oz).
Valve clearance, coldIN 0.15 to 0.25 mm (0.006 to 0.010 in); EX 0.25 to 0.35 mm (0.010 to 0.014 in); tappet lock nut 7 N·m (5 lb·ft) [0.7 kgf·m]
Timing beltCheck for cracks, damage, wear; replace if it deflects more than 10 mm (0.394 in) when pushed at the center

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. First 20 hours or 1 month

    Replace: engine oil, oil filter, oil drain plug gasket, gear case oil, gear case plug gaskets, propeller cotter pin

    Check: spark plugs, fuel filter

  2. Every 50 hours or 3 months

    Replace: gear case plug gaskets, propeller cotter pin

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

  3. Every 100 hours or 6 months

    Replace: engine oil, oil drain plug gasket, gear case oil, gear case plug gaskets, propeller cotter pin

    Check: spark plugs, fuel filter, water pump impeller, thermostat, anodes

  4. Every 200 hours or 1 year

    Replace: engine oil, oil filter, oil drain plug gasket, gear case oil, gear case plug gaskets, propeller cotter pin, water pump impeller

    Check: spark plugs, fuel filter, thermostat, anodes

Source: Tohatsu 4 Stroke MFS40A/50A service manual, OB No. 003-21067-0. Specs can change by model year and serial number, so always confirm your exact model from the serial tag on the clamp bracket.

Other Tohatsu guides