Yanmar 4LHA-HTP Operation Manual page 518

Chapter 6 Cooling Water System
1. Cooling Water System
1. Cooling Water System
The cooling water system is of the indirect sea water coded,
fresh water circulation type. The cylinders, cylinder heads,
turbocharger and exhaust manifold are cooled with fresh wa-
ter, and the lube oil cooler, air cooler and fresh water cooler
(heat exchanger) use sea water.
S e a water pumped in from the s e a by the s e a water pump
cools the lube oil in the lube oil cooler and then 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.
F r e s h water is pumped by the fresh water pump from the
fresh water tank to the cylinder jacket to cool the cylinders,
turbocharger and then 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.
Fresh water circuit
Cooling water
ft temperature switch
Thermostat
By pass—fl O
Fresh water pump
Sea water
I
4
Fresh water tank
Heat exchanger
(Fresh water cooler)
Cylinder head
- Cooling water
temperature sender ft
Cylinder block
Sea water pump
Kingston cock
H
The thermostat is closed when the fresh water 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 head exchanger, and it is then
cooled by the sea water in the tubes as it flows through the
cooling pipe. The temperature of the fresh.water is thus kept
within a constant range by the thermostat.
Filler cap
ft
Turbocharger
Sea water circuit
Sea water
6-1
t4LHA Serii
Fresh water sub tank
Mixing elbow
Marine gear oil cooler
2
Air cooler
Lube oil cooler