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Tohatsu MFS9.9A / MFS15A and MFS9.9B / MFS15B (carbureted) service guide

Oil, gear oil, spark plugs and the service schedule for the Tohatsu MFS9.9A / MFS15A and MFS9.9B / MFS15B (carbureted) (9.9 to 15 hp, four-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: MFS9.9A, MFS15A, MFS9.9B, MFS15B, types MF, EF, EP, S / L transom. 4-stroke twin, 328 mL (20.01 cu in), 59 x 60 mm, OHC, carburetor, CD ignition.

Quick answers

How much oil does a Tohatsu MFS9.9A / MFS15A and MFS9.9B / MFS15B take?
1,000 mL (1.1 US qt); dipstick upper level 1,000 mL, lower 750 mL (0.8 US qt).
What engine oil does a Tohatsu MFS9.9A / MFS15A and MFS9.9B / MFS15B use?
SAE 10W-30/40, API SF, SG, SH or SJ.
What gear oil does a Tohatsu MFS9.9A / MFS15A and MFS9.9B / MFS15B use, and how much?
Genuine gear oil or GL5, SAE #80 to #90. Quantity: 9.9A/15A: 200 mL (6.8 US fl oz) approx.; 9.9B/15B: 370 mL (12.5 US fl oz) approx.
What spark plug does a Tohatsu MFS9.9A / MFS15A and MFS9.9B / MFS15B use?
NGK DCPR6E. Gap: 0.8 to 0.9 mm (0.032 to 0.035 in); repair limit 1.2 mm.
How often should a Tohatsu MFS9.9A / MFS15A and MFS9.9B / MFS15B 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 12 months; Every 300 hours or 18 months; Every 400 hours or 24 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 MFS9.9A / MFS15A and MFS9.9B / MFS15B?
The factory schedule says to inspect it at 50 hours, 100 hours, 200 hours, 300 hours and 400 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 propeller nut torque on a Tohatsu MFS9.9A / MFS15A and MFS9.9B / MFS15B?
11.3 N·m (1.2 kg-m, 8.7 lb-ft).

Maintenance specs

Engine oilSAE 10W-30/40, API SF, SG, SH or SJ
Engine oil quantity1,000 mL (1.1 US qt); dipstick upper level 1,000 mL, lower 750 mL (0.8 US qt).
Engine oil drain plug23.7 N·m (2.4 kg-m, 17 lb-ft)
Gear oilGenuine gear oil or GL5, SAE #80 to #90
Gear oil quantity9.9A/15A: 200 mL (6.8 US fl oz) approx.; 9.9B/15B: 370 mL (12.5 US fl oz) approx.
Gear case drain screw and plugDrain screw 6.8 N·m (0.7 kg-m, 5 lb-ft); screw plug kit 6.8 N·m (0.7 kg-m, 5 lb-ft)
Spark plugNGK DCPR6E
Spark plug gap0.8 to 0.9 mm (0.032 to 0.035 in); repair limit 1.2 mm
Spark plug torque15 to 20 N·m (1.5 to 2.0 kg-m, 11 to 15 lb-ft)
ThermostatStarts opening 60 °C ± 1.5 °C (140 ± 3 °F); fully open 75 °C (167 °F); lift 3 mm (0.12 in) or more (hold 75 °C about 5 minutes before measuring)
Propeller nut11.3 N·m (1.2 kg-m, 8.7 lb-ft)
Valve clearanceIN 0.13 to 0.17 mm (0.005 to 0.007 in); EX 0.18 to 0.22 mm (0.007 to 0.008 in); tappet lock nut 6 to 8 N·m (4.4 to 5.8 lb-ft)
Timing beltCheck tension and appearance; replace if worn, cracked or lengthened (no deflection spec)

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, anodes

  3. Every 100 hours or 6 months

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

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

  4. Every 200 hours or 12 months

    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, anodes

  5. Every 300 hours or 18 months

    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, anodes

  6. Every 400 hours or 24 months

    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, 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 service manual 9.9A/15A and 9.9B/15B, copyright 2007. 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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