Cooling Water System - Yanmar 3YM30 Service Manual

9. Cooling water system

9. Cooling water system
9.1 Cooling water system
The cooling water system is of the indirect seawater cooled, fresh water circulation type. The cylinders,
cylinder heads and exhaust manifold are cooled with fresh water, and fresh water cooler (heat
exchanger) use seawater.
Seawater pumped in from the sea by the seawater pump goes to the heat exchanger, where it cools the
fresh water. Then it is sent to the mixing elbow and is discharged from the ship with the exhaust gas.
Fresh water is pumped by the fresh water pump to the cylinder jacket to cool the cylinders and the
cylinder head. The fresh water pump body also serves as a discharge passageway (line) at the cylinder
head outlet and is fitted with a thermostat.
The thermostat is closed when the fresh water pump temperature is low, immediately after the engine is
started and during low load operation, etc. Then the fresh water flows to the fresh water pump inlet, and
is circulated inside the engine without passing through the heat exchanger.
When the temperature of the fresh water rises, the thermostat opens, fresh water flows to the heat
exchanger, and it is then cooled by the seawater in the tubes as it flows through the cooling pine. The
temperature of it flows through the cooling pine. The temperature of the fresh water is thus kept within a
constant range by the thermostat.
Seawater circuit
Fresh water circuit
Thermostat
Fresh water pump
Sea cock
P
P
Seawater pump
Heat exchanger
Cylinder head
Cylinder block
157R1
Coolant recovery tank
Mixing
elbow