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Tohatsu MFS75A / MFS90A / MFS100A / MFS115A (2.0 L four-stroke) service guide

Oil, gear oil, spark plugs and the service schedule for the Tohatsu MFS75A / MFS90A / MFS100A / MFS115A (2.0 L four-stroke) (75 to 115 hp, four-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: MFS75A, 90A, 100A and 115A, EHT (tiller) and EPT (remote), L and UL transoms; 4 cylinder SOHC, 1995 cm³ (121.6 cu in), fuel injection.

Quick answers

How much oil does a Tohatsu MFS75A / MFS90A / MFS100A / MFS115A take?
4,200 mL (4.44 US qt) with filter; 4,000 mL (4.23 US qt) without filter. Dipstick lower limit 2,200 mL (2.32 US qt).
What engine oil does a Tohatsu MFS75A / MFS90A / MFS100A / MFS115A use?
Tohatsu 4-Stroke Engine Oil, API SH, SJ or SL, SAE 10W-30 or 10W-40.
What gear oil does a Tohatsu MFS75A / MFS90A / MFS100A / MFS115A use, and how much?
Tohatsu Gear Oil, API GL-5, SAE #80-90. Quantity: Same for standard and counter rotation; fill through the lower plug hole.
What spark plug does a Tohatsu MFS75A / MFS90A / MFS100A / MFS115A use?
NGK LKR6E.
How often should a Tohatsu MFS75A / MFS90A / MFS100A / MFS115A be serviced?
The factory schedule lists: Initial 20 hours or 1 month; 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 MFS75A / MFS90A / MFS100A / MFS115A?
The factory schedule says to replace it at 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 idle speed of a Tohatsu MFS75A / MFS90A / MFS100A / MFS115A?
700 r/min (neutral and dead slow in forward).
What is the propeller nut torque on a Tohatsu MFS75A / MFS90A / MFS100A / MFS115A?
35 N·m (26 lb·ft) [3.5 kgf·m].

Maintenance specs

Engine oilTohatsu 4-Stroke Engine Oil, API SH, SJ or SL, SAE 10W-30 or 10W-40
Engine oil quantity4,200 mL (4.44 US qt) with filter; 4,000 mL (4.23 US qt) without filter. Dipstick lower limit 2,200 mL (2.32 US qt)
Oil filter18 N·m (13 lb·ft) [1.8 kgf·m] with wrench P/N 3AC-99090-0; Oil filter bolt M20 x 1.5: 40 N·m (29 lb·ft) [4 kgf·m]
Oil pan drain bolt (M14 x 1.5)24 N·m (18 lb·ft) [2.4 kgf·m]; new gasket, oil on the sealing area
Gear oilTohatsu Gear Oil, API GL-5, SAE #80-90
Gear oil quantitySame for standard and counter rotation; fill through the lower plug hole
Gear oil plugs (M8 x 1.25)4 N·m (3 lb·ft) [0.4 kgf·m]; new gaskets
Gear case leak test0.05 MPa (7 psi) [0.5 kgf/cm²], oil drained, held 10 seconds; do not go over
Spark plugNGK LKR6E
Spark plug torque18 N·m (13 lb·ft) [1.8 kgf·m]
Idle speed700 r/min (neutral and dead slow in forward)
ThermostatStarts to open 60 ± 1.5 °C (140 °F); fully open 75 °C (167 °F); lift 4.5 mm (0.18 in) or more
Cooling water pressure (reference)Neutral: 700 r/min 5 kPa (1 psi); 850 r/min 15 kPa (2 psi); 2000 r/min 35 kPa (5 psi). Forward: 3000 to 6000 r/min 40 kPa (6 psi). T-fitting in the hose between vapor separator and check port
AnodesCooling passage (cylindrical) anode screw 2.5 N·m (1.84 lb·ft), ThreeBond 1342; anode plug M16 18 N·m (13 lb·ft). Replace when worn to 2/3 of new size.
Propeller nut (M16 x 1.5)35 N·m (26 lb·ft) [3.5 kgf·m]
Power trim and tilt fluidATF DEXRON III; 682 mL (23.1 fl oz); full when fluid spills at the cap, motor tilted fully up. Reservoir cap 0.7 N·m (0.5 lb·ft)
Valve clearance, coldIN 0.10 to 0.20 mm (0.004 to 0.008 in); EX 0.15 to 0.25 mm (0.006 to 0.010 in); lock nut 7 N·m (5 lb·ft) [0.7 kgf·m]
Timing beltCheck inner and outer surfaces for cracks, damage, wear; replace if necessary (no deflection spec). Tensioner bolt 40 N·m (30 lb·ft) [4.1 kgf·m]

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

    Check: fuel filter

  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: spark plugs, fuel filter, anodes

  3. 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

  4. Every 400 hours or 2 years

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

    Check: spark plugs, thermostat, 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 MFS75A/90A/100A/115A/140A/150A service manual, OB No. 003-21075-3BE1. 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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