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Tohatsu MFS 4 / 5 / 6 (A2 and D) service guide

Oil, gear oil, spark plugs and the service schedule for the Tohatsu MFS 4 / 5 / 6 (A2 and D) (4 to 6 hp, four-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: MFS 4D, 5D and 6D (dual tank, separate tank, and 6D Sail Pro) and the earlier MFS 4A2, 5A2S, 6A2S. Same basic engine in both: 1 cylinder, 123 mL (7.5 cu in), bore x stroke 59 x 45 mm, OHV, carburetor, CD ignition, trochoid oil pump, 450 mL oil, 195 mL gear oil.

Quick answers

How much oil does a Tohatsu MFS 4 / 5 / 6 take?
450 mL (15.2 fl oz) to the upper mark; lower mark 350 mL. No oil filter.
What engine oil does a Tohatsu MFS 4 / 5 / 6 use?
D: 4-stroke engine oil API SH, SJ or SL, SAE 10W-30 or 10W-40, NMMA FC-W 10W-30/40. A2: API SF, SG or SH, SAE 10W-30/40.
What gear oil does a Tohatsu MFS 4 / 5 / 6 use, and how much?
Hypoid gear oil, API GL-5, SAE #80-90 (genuine gear oil). Quantity: 195 mL (6.6 fl oz). Fill through the lower plug hole until oil spills from the upper hole without bubbles.
What spark plug does a Tohatsu MFS 4 / 5 / 6 use?
NGK DCPR6E. Gap: 0.8 to 0.9 mm (0.031 to 0.035 in); limit 1.2 mm (0.047 in).
How often should a Tohatsu MFS 4 / 5 / 6 be serviced?
The factory schedule lists: D models, initial 20 hours or 1 month; D models, every 50 hours or 3 months; D models, every 100 hours or 6 months; D models, every 200 hours or 1 year; A2 models, every 300 hours or 18 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 MFS 4 / 5 / 6?
The factory schedule says to inspect it at 50 hours, 100 hours, 200 hours and 300 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 MFS 4 / 5 / 6?
D: neutral 1,300 r/min, trolling in forward 1,150 r/min (warm engine). A2: idle 1,300 r/min, trolling 1,100 r/min.
What is the propeller nut torque on a Tohatsu MFS 4 / 5 / 6?
D: spline drive; tighten the nut, then turn it on to line up a groove with the hole and fit the split pin. A2: nut and split pin.

Maintenance specs

Engine oilD: 4-stroke engine oil API SH, SJ or SL, SAE 10W-30 or 10W-40, NMMA FC-W 10W-30/40. A2: API SF, SG or SH, SAE 10W-30/40
Engine oil quantity450 mL (15.2 fl oz) to the upper mark; lower mark 350 mL. No oil filter
Oil drain bolt (M10 x 1.25)D: 18 N·m (13 lb·ft) [1.8 kgf·m]. A2: 15 to 20 N·m (1.5 to 2.0 kg·m, 11 to 14.5 ft·lb)
Gear oilHypoid gear oil, API GL-5, SAE #80-90 (genuine gear oil)
Gear oil quantity195 mL (6.6 fl oz). Fill through the lower plug hole until oil spills from the upper hole without bubbles
Gear oil plugs (M8 x 1.25)D: 4 N·m (3 lb·ft) [0.4 kgf·m]; new gaskets.
Gear case leak test0.049 MPa (7 psi) [0.5 kgf/cm²], must hold for 10 seconds; do not go over this pressure
Spark plugNGK DCPR6E
Spark plug gap0.8 to 0.9 mm (0.031 to 0.035 in); limit 1.2 mm (0.047 in)
Spark plug torque (M12 x 1.25)D: 18 N·m (13 lb·ft) [1.8 kgf·m], hand tight first. A2: 15 to 20 N·m (1.5 to 2.0 kg·m, 11 to 14 ft·lb)
Idle speedD: neutral 1,300 r/min, trolling in forward 1,150 r/min (warm engine). A2: idle 1,300 r/min, trolling 1,100 r/min
ThermostatD: starts to open 50 to 54 °C (121 to 129 °F); lift 3.0 mm (0.12 in) or more at 63 to 67 °C (146 to 154 °F). A2: starts to open 52 ± 2 °C (125 ± 4 °F); lift 3 mm (0.12 in) or more
AnodeReplace when reduced to 2/3 of a new part; retighten the anode bolt at every inspection; do not paint or oil it.
Propeller nutD: spline drive; tighten the nut, then turn it on to line up a groove with the hole and fit the split pin. A2: nut and split pin
Valve clearance, coldIN 0.06 to 0.14 mm (0.0024 to 0.0055 in); EX 0.11 to 0.19 mm (0.0043 to 0.0075 in); piston at TDC compression. Pivot adjust nut: D 10 N·m (7 lb·ft) [1.0 kgf·m]; A2 9 to 11 N·m (6.5 to 8 ft·lb)

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. D models, initial 20 hours or 1 month

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

    Check: spark plugs, fuel filter

  2. D models, every 50 hours or 3 months

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

    Check: fuel filter, water pump impeller, anodes

  3. D models, 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, anodes

  4. D models, every 200 hours or 1 year

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

    Check: spark plugs, fuel filter, thermostat, anodes

  5. A2 models, every 300 hours or 18 months

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

    Check: spark plugs, fuel filter, 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 4 stroke MFS 4D / 5D / 6D service manual, OB No. 003-21034-4; Tohatsu 4-Stroke 4 / 5 / 6 service manual, MFS 4A2 / 5A2 / 6A2. 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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