Tohatsu 4 Stroke MFS 2/2.5/3.5A Outboards Service Manual, Page 55Get this manual
Maintenance 22) Inspection of Thermostat
1Remove bolts, and then thermostat cap and thermostat 2
Hang thermostat in the water contained in vesselPut thermometer in the water, and warm up water to measure valve opening temperaturePut piece of thread in the closed valve gap and hang it in the waterValve opening moment can be known when thermostat is released to drop due to opening with rise of temperatureValve Opening Temperature52C2C(125F4F) (Valve starts to open at this temperature