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Tohatsu MFS 6 / 8 / 9.8 / 9.9 EFI (C) service guide

Oil, gear oil, spark plugs and the service schedule for the Tohatsu MFS 6 / 8 / 9.8 / 9.9 EFI (C) (6 to 9.9 hp, four-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: MFS 6CZ, 8C, 9.8C and 9.9CY (anode list also names the 9.9CX), types MF, EF, EFT, EP, EPT: 2 cylinder, 209 mL (12.7 cu in), bore x stroke 55 x 44 mm, OHC with timing belt, fuel injection with ECU.

Quick answers

How much oil does a Tohatsu MFS 6 / 8 / 9.8 / 9.9 EFI take?
800 mL (0.8 US qt) to the upper mark; lower mark 600 mL. No oil filter (oil strainer inside the engine).
What engine oil does a Tohatsu MFS 6 / 8 / 9.8 / 9.9 EFI use?
4-stroke engine oil API SH, SJ or SL; SAE 10W-30 or 10W-40.
What gear oil does a Tohatsu MFS 6 / 8 / 9.8 / 9.9 EFI use, and how much?
Tohatsu gear oil, API GL-5, SAE 80-90. Quantity: Fill through the lower plug hole until it flows from the upper hole.
What spark plug does a Tohatsu MFS 6 / 8 / 9.8 / 9.9 EFI use?
NGK DCPR6E (or equivalent). 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 6 / 8 / 9.8 / 9.9 EFI be serviced?
The factory schedule lists: Every 50 hours or 3 months; Every 100 hours or 6 months; Every 200 hours or 1 year; Every 400 hours or 2 years. 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 6 / 8 / 9.8 / 9.9 EFI?
The factory schedule says to replace it at 200 hours and 400 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 MFS 6 / 8 / 9.8 / 9.9 EFI?
Neutral 900 r/min; dead slow in forward 900 r/min (warm engine).
What is the propeller nut torque on a Tohatsu MFS 6 / 8 / 9.8 / 9.9 EFI?
12 N·m (9 lb·ft) [1.2 kgf·m], then line up a groove and fit the split pin.

Maintenance specs

Engine oil4-stroke engine oil API SH, SJ or SL; SAE 10W-30 or 10W-40
Engine oil quantity800 mL (0.8 US qt) to the upper mark; lower mark 600 mL. No oil filter (oil strainer inside the engine)
Gear oilTohatsu gear oil, API GL-5, SAE 80-90
Gear oil quantityFill through the lower plug hole until it flows from the upper hole
Gear oil plugs (M8 x 1.25, cross-head screw)4 N·m (3 lb·ft) [0.4 kgf·m]; new gaskets
Gear case leak test0.05 MPa (7 psi) [0.5 kgf/cm²]
Spark plugNGK DCPR6E (or equivalent)
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)18 N·m (13 lb·ft) [1.8 kgf·m]
Idle speedNeutral 900 r/min; dead slow in forward 900 r/min (warm engine)
AnodesReplace when reduced to 2/3 of a new one; retighten the anode bolts at every inspection; do not oil or paint. Cooling water passage anode: anode screw 2.5 N·m (1.84 lb·ft) [0.25 kgf·m] with ThreeBond 1342; anode plug M16 18 N·m (13 lb·ft) [1.8 kgf·m], new O-ring
Propeller nut (M10 x 1.25)12 N·m (9 lb·ft) [1.2 kgf·m], then line up a groove and fit the split pin
Valve clearance, coldIN 0.10 to 0.15 mm (0.004 to 0.006 in); EX 0.20 to 0.24 mm (0.008 to 0.0095 in); tappet adjustment lock nut M6: 7 N·m (5 lb·ft) [0.7 kgf·m]
Timing beltReplace if it deflects more than 10 mm (0.394 in) when pressed at the center. Drive (timing) pulley nut M30: 64 N·m (47 lb·ft) [6.4 kgf·m]; camshaft pulley bolt 11 N·m (8 lb·ft)

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. Every 50 hours or 3 months

    Replace: gear case plug gaskets, propeller cotter pin

    Check: gear case oil, water pump impeller, anodes

  2. Every 100 hours or 6 months

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

    Check: fuel filter, water pump impeller, anodes

  3. 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: fuel filter, thermostat, anodes

  4. Every 400 hours or 2 years

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

    Check: fuel filter, thermostat, anodes

Source: Tohatsu 4 stroke 6/8/9.9 service manual, MFS 6CZ / 8C / 9.8C / 9.9CY. 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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