Thermostat; Functioning Of Thermostat; Thermostat Construction; Characteristics Of Thermostat - Yanmar 3YM30 Sevice Manual

9. Cooling water system

9.6 Thermostat

9.6.1 Functioning of thermostat

The thermostat opens and closes a valve according to changes in the temperature of the fresh water
inside 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 outlet
line 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 portion
of the water is sent to the heat exchanger and cooled by seawater, the other portion going from the
bypass line to the fresh water pump intake.
The bypass line is closed off as the thermostat valve opens and is completely closed when the fresh
water temperature reaches 81.5
exchanger.

9.6.2 Thermostat construction

The thermostat used in this engine is of the wax pellet
type, with a solid wax pellet located in a small chamber.
When the temperature of the cooling water rises, the
wax melts and increases in volume. This expansion and
construction is used to open and close the valve.

9.6.3 Characteristics of thermostat

Opening temperature
Full open temperature
Valve lift at full open

9.6.4 Thermostat inspection

Remove the thermostat cover on top of the fresh water
pump and take out the thermostat. Clean off scale and
rust and inspect, and replace if the characteristics
(performance) have changed, or if the spring is broken,
deformed ar corroded.

9.6.5 Testing the thermostat

Refer to 2.5 in chapter 2.
C (valve lifts 4 mm (0.1575 in)), sending all of the water to the heat
°
69.5-72.5°C
85°C
8 mm or more
169
Thermostat cover
Thermostat
Fresh water pump body