1970 Johnson 115 HP Outboard Motor Service manual, Page 69Get this manual
IMPELLER AT
power head and cooling system temperatures each 145 the Vernatherm control ele ment opens the the rmostat 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 Utrough 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
Figure 6- 3Impeller Positions