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Tohatsu MFS9.9C / MFS15C / MFS20C (carbureted, 2012) service guide

Oil, gear oil, spark plugs and the service schedule for the Tohatsu MFS9.9C / MFS15C / MFS20C (carbureted, 2012) (9.9 to 20 hp, four-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: MFS9.9C, MFS15C, MFS20C, types MF, EF, EFT, EP, EPT, S / L / UL transom. 4-stroke twin, 351 cm³ (21.41 cu in), 61 x 60 mm, OHC, carburetor with acceleration pump, CD ignition.

Quick answers

What engine oil does a Tohatsu MFS9.9C / MFS15C / MFS20C use?
4-stroke engine oil, API SE, SF, SG, SH, SJ, SL or SM; SAE 10W-30 or 10W-40; NMMA FC-W certified 10W-30/40.
What gear oil does a Tohatsu MFS9.9C / MFS15C / MFS20C use, and how much?
Hypoid gear oil, API GL-5, SAE #90 (schedule remark: genuine gear oil GL5, SAE 80 to 90). Quantity: 370 cm³ (12.5 fl oz); fill from the lower plug hole until oil comes out the upper hole.
What spark plug does a Tohatsu MFS9.9C / MFS15C / MFS20C 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 MFS9.9C / MFS15C / MFS20C be serviced?
The factory schedule lists: Initial 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 MFS9.9C / MFS15C / MFS20C?
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 MFS9.9C / MFS15C / MFS20C?
950 ± 30 r/min in neutral after 5 minutes warm-up; 950 r/min idle, 900 r/min trolling in gear.
What is the propeller nut torque on a Tohatsu MFS9.9C / MFS15C / MFS20C?
12 N·m (9 lb·ft) [1.2 kgf·m], then cotter pin.

Maintenance specs

Engine oil4-stroke engine oil, API SE, SF, SG, SH, SJ, SL or SM; SAE 10W-30 or 10W-40; NMMA FC-W certified 10W-30/40
Oil filter18 N·m (13 lb·ft) [1.8 kgf·m] with oil filter wrench P/N 3AC-99090-0; oil the O-ring; change 5 minutes or more after stopping
Engine oil drain bolt24 N·m (17 lb·ft) [2.4 kgf·m], M14 x 1.5; oil the washer
Gear oilHypoid gear oil, API GL-5, SAE #90 (schedule remark: genuine gear oil GL5, SAE 80 to 90)
Gear oil quantity370 cm³ (12.5 fl oz); fill from the lower plug hole until oil comes out the upper hole
Gear oil plugsNew gaskets on both plugs; attach the upper plug first.
Gear case leak test0.069 MPa (10 psi) [0.7 kgf/cm²] through the upper plug hole, must hold 10 seconds; do not go higher
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 speed950 ± 30 r/min in neutral after 5 minutes warm-up; 950 r/min idle, 900 r/min trolling in gear
ThermostatStarts opening 60 ± 1.5 °C (140 ± 3 °F); lift 3.0 mm (0.12 in) or more at 75 °C (167 °F); cover bolt 6 N·m (4 lb·ft) [0.6 kgf·m], new gasket
AnodesReplace when reduced to 2/3 of new size; do not paint or oil; retighten the anode bolt at every inspection
Propeller nut12 N·m (9 lb·ft) [1.2 kgf·m], then cotter pin
Valve clearance, coldIN 0.13 to 0.17 mm (0.0051 to 0.0067 in); EX 0.18 to 0.22 mm (0.0071 to 0.0087 in); lock nut 7 N·m (5 lb·ft) [0.7 kgf·m]
Timing beltInspect for cracks, damage and wear; replace if worn, damaged or stretched (no deflection spec). Align "1" on the cam pulley with the mark on the head for #1 TDC.

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 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. Every 50 hours or 3 months

    Replace: gear case plug gaskets, propeller cotter pin

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

  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 service manual 4st 9.9/15/20 2012, OB No. 003-21062-1. 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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