Honda BF9.9A-BF15A Outboard Motors Shop Manual., Page 124Get this manual
MAJOR MECHANISMS COOLING SYSTEM
aCOOLING PATH
Water is taken through the intake holes (main intake hole and emergency intake hole) on the gear case, and pum ed upward by the water pump, to each jacket such as water tube, exhaust pipe (Ki) ,water jacket around the cvlinderd) cylinder head and inlet manifold (J3) Thus cooling each part, the water goes through thermostat and cools oil case before passing the extension case and is then exhausted through the propeller bossSome of the water pumped to the exhaust pipe ,goes through the inlet manifold and is exhausted through the cooling water identification holeIt is also pumped into the exhaust pipe cool the exhaust gas
bWATER PUMP
The water pump installed in the gear caseIt is an impeller type pump driven by pinion shaft
cTHERMOSTAT
The thermostat, also attached to the water jacket (inlet manifold) outlet, maintains the water temperature inside the water jacket in constant range by opening and closing the valve according the temperature of engine cooling waterI the temperature is too low the thermostat closes the valve and the water inside the jacket is held until the temperature reaches certain valueThe water pump then will again be activated to pump water and exhaust it through the valve hole of the thermostat, the cooling water identification hole, the exhaust pipe cooling hole and the impeller housing hole