COOLING SYSTEM
-
Description
CO
-3
The cooling system
is
composed of the water
jacket (inside the cylinder block and cylinder head),
radiator, water pump, thermostat, cooling fan,
hoses and other components. Coolant which
is
heated in the water jacket
is
pumped to the radia-
tor, where
it
is
cooled by the cooling fan and the
vehicle windstream. Coolant which has been
cooled
is
then sent back to the engine by the water
pump, where
it
cools the engine. The water jacket
is
a network of channels in the shell of the cylinder
block and cylinder head through which coolant
passes.
It
is
designed to provide adequate cooling
of the cylinders and combustion chambers which
become the hottest during engine operation.
RADIATOR
The radiator performs the function of cooling
the coolant which has passed through the water
jacket and become hot, and
it
is
mounted in the
front of the vehicle. The radiator consists of an
upper tank and lower tank, and
a
core which con-
nects the two tanks. The upper tank contains an
inlet for coolant from the water jacket and
a
filler
inlet.
It
also has
a
hose through which excess
coolant or steam can flow. The lower tank has an
outlet and drain cock for the coolant. The core
contains many tubes and cooling fins through
which coolant flows from the upper tank to the
lower tank so that coolant has been heated up
as
it
passes through the water jacket
is
cooled here by
the air sucked through the radiator by the cool-
ing fan,
as
well
as
by the wind generated by the.
vehicle's travel. Models with an automatic trans-
mission include an automatic transmissions fluid
cooler built into the lower tank of the radiator.
RADIATOR CAP
The radiator cap
is
a
pressure type cap which
seals the radiator, resulting in pressurization of the
radiator as the coolant expands. The pressuriza-
tion prevents the coolant from boiling even when
the coolant temperature exceeds 100" C (21 2"
F).
A
relief valve (pressurization valve) and
a
vacuum
valve (negative pressure valve) are built into the
radiator cap. When the pressure generated inside
the cooling system exceeds the limit (coolant tem-
perature: 1 10
-
1 20°C, 230
-
248" F, pressure;
0.3
-
1.0 kg/cm2, 4.3
-
14.2 psi, 29.4
-
98.1 kPa)
the relief valve
is
opened by the pressure and lets
steam escape through the overflow pipe. The
vacuum valve opens to allow atmospheric air to
enter to alleviate the vacuum which develops in the
cooling system after the engine
is
stopped and the
coolant temperature drops. The valve's opening
allows the pressure in the cooling system to return
to the reservoir tank.
RESERVOIR TANK
*
The reservoir tank
is
used to catch coolant
which overflows the cooling system
as
a
result of
volumetric expansion when the coolant
is
heated.
When the cod~ant temperature drops, the coolant
in the reservoir tank returns to the radiator, thus
keeping the radiator full at
all
times and avoiding
needless coolant loss. To find out if the coolant
needs to
be
replenished, check the reservoir tank
level.
WATER PUMP
The water pump
is
used for forced circulation of
coolant through the cooling system.
It
is
mounted
on the front of the cylinder block and driven by
a
drive belt.
THERMOSTAT
The thermostat has
a
wax type by-pass valve and
is
mounted in the water outlet housing. The
thermostat
is
a
type of automatic valve operated
by fluctuations
in
the coolant temperature. This
valve closes when the coolant temperature drops,
preventing the circulation of coolant through the
radiator and thus permitting the engine to warm up
rapidly. The valve opens when the coolant temper-
ature has risen, allowing the circulation of coolant.
Wax inside the thermostat expands when heated
and contracts when cooled. Heating the wax thus
generates pressure which overpowers the force of
the spring which keeps the valve closed, thus
opening the valve. When the wax cools,
its
con-
traction causes the force of the spring to take
effect once more, closing the valve. The thermo-
stat in this engine operates
at
a
temperature of
88°C (191°F).
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