1971 Evinrude StarFlite 100 HP Outboards Service Manual, PN 4753, Page 67Get this manual
IMPELLER AT
power head and cooling system temperatures reach 145F the Vernatherm control element opens the thermostat valve, allowing heated water to pass through the water dischargeThe drop in cooling system pressure caused by the opening of the thermostat valve causes the pressure valve to close, preventing cooling system water from being recirculated through the water pump and allowing fresh water to be drawn through the water intakeThis action provides perfect water jacket temperatures in any water and any weatherLOW SPEED HIGH SPEED
WATER PUMP Water for cooling the power head is circulated by the water pump, located at the top of the gearcase and driven by the driveshaftThe pump consists of synthetic rubber impeller which is keyed to the driveshaft, and the pump housing which is offset from center with respect to the driveshaftBecause the housing is offset, the impeller blades flex as they rotate, varying the space between themThe pump inlet port, located in the stainless steel plate which forms the lower part of the pump housing, is open to the blades when the space between them is increasingThe pump outlet port, in the impeller housing, is open to the blades when the space between them.is decreasingThus at low speeds the impeller works as displacement resistance keeps the blades from flexing, and the pump becomes centrifugalSee Figure 6-3GEARCASE