Honda BF75, BF100, BF8A Outboard Motors Shop Manual, Page 109Get this manual
CONSTRUCTION AND FUNCTION
COOLING SYSTEM
Water is drawn into the water pump (2) from the port screen (1) under the anticavitation plateIt is then pumped through water pipe (3) into the water jackets (4) to cool the entire length of each cylinder wallAfter cooling the cylindersthe water is directed into the cylinder head (6)and from there back outside through the exhaust pipe (7) with the exhaust gasesA thermostat (5) located at the outlet of the cylinder jacket opens and closes to the water temperature from the cylinder jacket to maintain constant cooling water temperature When the water is coldit cannot pass into the cylinder headthat is, it just circulates through the intake manifold (11) The water from the pump outlet is directly returned outside through the water check pipe (9) and exhaust pipe via the bypass tube (8) The pump is an impeller type and is located on the gear case It is driven by the pinion shaft (10)