9. Cooling water system1699.6 Thermostat9.6.1 Functioning of thermostatThe thermostat opens and closes a valve according to changes in the temperature of the fresh waterinside the engine, controlling the volume of water flowing to the heat exchanger from the cylinder head,and in turn maintaining the temperature of the fresh water in the engine at a constant level.The thermostat is bottom bypass type. It is located in a position connected with the cylinder head outletline at the top of the top of fresh water pump unit.When the fresh water temperature exceeds the above temperature, the thermostat opens, and a portionof the water is sent to the heat exchanger and cooled by seawater, the other portion going from thebypass line to the fresh water pump intake.The bypass line is closed off as the thermostat valve opens and is completely closed when the freshwater temperature reaches 81.5°C (valve lifts 4 mm (0.1575 in)), sending all of the water to the heatexchanger.9.6.2 Thermostat constructionThe thermostat used in this engine is of the wax pellettype, with a solid wax pellet located in a small chamber.When the temperature of the cooling water rises, thewax melts and increases in volume. This expansion andconstruction is used to open and close the valve.9.6.3 Characteristics of thermostat9.6.4 Thermostat inspectionRemove the thermostat cover on top of the fresh waterpump and take out the thermostat. Clean off scale andrust and inspect, and replace if the characteristics(performance) have changed, or if the spring is broken,deformed ar corroded.9.6.5 Testing the thermostatRefer to 2.5 in chapter 2.Opening temperature 69.5-72.5°CFull open temperature 85°CValve lift at full open 8 mm or moreThermostat coverThermostatFresh water pump body
