2007-2009 Yamaha F15/F20 Outboard Service Manual, Page 300Get this manual
7COOLING SYSTEM 1) ANODE LOCATION
New anode for cooling-water passages is used for better anti-corrosionThe external anodes are located as shown in the photo
Fig24 External anode location The internal anodes are located to the thermostat cover and cylinder body
2) COOLING-WATER FLOW DIAGRAM
HotWarm water Thermostat Cylinder body Flushing attachment Cool water Water tap