D439E Service Manual 2. Engine Mechanical System (D439E)
117
Cooling System
Description
Cooling System
Water pump cools down the engine by circulating
the coolant forcibly as shown In the illustration below.
Water Pump
A : from the radiator
B : from the thermostat
C : to the crank case
Water pump, a centrifugal type, is driven by the V-
belt from tile crankshaft pulley. A unit seal is
installed between impeller and water pump that
prevents leakage of coolant. There is a drain hole
provided at the bottom of the water pump case,
which ensures that water should leak from the unit
seal does not enter bearings. The water pump is
mounted on the timing gear case provided with a
suction pipe and swirl chamber.
An Impeller pressed fit into the one end of water
pump shaft, has tile combination blade, which feeds
coolant under pressure into the engine.
Thermostat
A : form cylinder head B : to radiator
C : to water pump
1. The thermostat. of a bottom bypass configuration
has a valve controlled by a special wax enclosed
In a pellet
2. Tile wax changes from solid to liquid as it is
heated involving volumetric change for regulation
the flow of coolant.
Tile valve position changes depending on the
coolant temperatures regulate the flow rate of
coolant into the radiator and water pump (bypass
side), thus controlling coolant temperature.
A : air B : water
3. A Jiggle valve is installed in the air plug hole of
thermostat, which heats up the coolant
temperature rapidly to put the engine temperature
to the normal one. When engine stops, and
coolant flows as jiggle valve falls down by its
weight so that air in the engine is led to radiator
through the clearance between the jiggle valve
and the breather hole.
When the engine starts coolant flow into the
radiator and Jiggle valve is pushed up by the
water pressure As a result. valve covers tile air
plug hole to prevent the coolant from leaking
through the hole
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