Radiator Cap; Reservoir Tank; Water Pump; Thermostat - Toyota 3b Repair Manual

STEM
_
Description
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 pressurization
prevents
the coolant from boiling
even
when
the
coolant temperature exceeds
tOOoC (212oF). A
relief
valve (pressurization valve) and
a
vacuum
valve (negative pressure valve) are
built into
the
radiator cap. The relief valve opens and lets
steam
escape through the overflow pipe when the
pres_
sure generated inside the cooling system
exceeds
the limit
(coolant temperature: t
iO
_
12OoC,
2gO
-.248oF,
pressure: O.7b
-
1.OS kg,zcm2,
1O.7
_
14.9 psi, 73.S
-
103.O kpa). The vacuum
vatve
opens
to
let in
atomspheric air to
alleviate the
vacuum which develops in the coolant system
after
the engine is
stopped and
the coolant temperature
drops.
RESERVOIR TANK
The reservoir tank is
used
to catch coolant which
overflows the cooting system as
a
result of
volu_
metric expansion when the coolant is
heated.
The
coolant in the reservoir tank returns to the radiator
when the coolant temperature
drops, thus
keeping
the
radiator full
at all times and avoiding
n"edt"sl
coolant loss. To
find out if the
coolant needs to
be
replenished, check the coolant level in the reservoir
tank.
WATER PUMP
The water pump is
used for forced circulation of
coolant through the
cooling system. lt
is
mounted
on the front of the cylinder biock and driven by
a
V-ribbed belt.
THERMOSTAT
The thermostat has
a
wax type
bypass 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,
pre_
venting the
circulation
of
coolant through
the
radiator. Because
the
bypass valve is
open
the
coolant inside
the
engine circutates inside
the
engine only, thus permitting the engine to warm
up
rapidly. When
the
coolant temperJture has risen,
the thermostat valve
opens and
the
bypass valve
closes allowing
the circulation of
coolant through
the engine and radiator. Wax inside the thermostat
expands when
heated and contracts when
cooled.
Heating
the wax thus
generates pressure which
overpowers
the
force of the
spring keeping
the
valve closed,
thus
opening the valie. Whei
the
wax cools, its contraction causes the force
of the
spring to take effect once more, closing the
valve.
ln this
engine
two
types
of
thermosta-t
are
used
which
operate at temperatures of g2oc (l
gOoF)
and
88oC
(1
gOoF)
respectively.
l-t