1968 Evinrude Starflite 100 HP outboards Service Manual, Page 45Get this manual
When the power head and cooling system temperatures reach 145 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 weatherTEMPERATURE SWITCH heat switch, installed in the head of the No3 cylinder, is in series with warning light on the control panelShould an irregularity develop in the cooling system and cause abnormal water jacket temperatures, the switch closes the warning light circuitSee Figure 5-5The switch may be checked by submerging it in hot oilUsing test light to check the contacts and thermometer to check oil temperature, the contacts should be found to close at temperature of 211 60 and open at 175 7See Figure 5-6 Figure 5-5Removing Heat Switch