Chevrolet 70 1969 Series, Shop Manual

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ENGINE C O O LIN G SYSTEM 6K-6
5. If engine unit tests satisfactory under above
conditions, check following items according to
nature of difficulty.
a. If gauge does not register when ignition or
control switch is turned on: This may be caused
by a break in the circuit between the gauge and the
switch or a short between this lead and ground.
b. If gauge shows high temperature under all
conditions; wire leading from gauge to engine unit
is shorted to ground.
c. If gauge registers a low temperature under
all conditions, wire between gauge and engine unit
is broken.
Do not attempt to repair either the engine unit
or the gauge. When installing new engine unit, do
not use thread compound on unit threads, as this
will increase electrical resistance of unit and
cause faulty reading on gauge.
ENGINE OVERHEAT ALARM
Overheat alarm switch is located near the
engine unit of water temperature indicator. Refer
to figure 2 or 3 for appropriate location of engine
overheat alarm.
N O T E : Electrical wire end of overheat switch
is retained by screw; whereas, wire end for temp­
erature indicator is retained by a nut.
The alarm system is interconnected to a tell­
tale light and, on some vehicles, to a buzzer. The
purpose of this system is to signal the driver when
engine temperature exceeds a safe range. Refer to
applicable wiring diagram in Section 12 for alarm
system circuit. Overheat temperature switch is
not repairable and must be replaced as an assem­
bly or unit.
T E S T IN G E N G IN E UNIT A N D CIRCUIT
N O T E : Before testing engine unit, make the
following circuit tests.
Circuit Tests
1. Disconnect wire at engine unit.
2. Connect a test light consisting of a 2-
candlepower 12 volt bulb and a pair of test leads
in circuit by clipping one lead to a hot terminal
and other lead to body of engine unit. If bulb does
not light, check for presence of sealing compound,
oil or paint around threads of unit. Remove insul­
ating substance and repeat test. Make sure unit is
properly grounded before proceeding with tests.
3. Remove test lead from body of engine unit
and connect lead to terminal of unit. Then provid­
ing engine water temperature is not exceeding
switch setting, and the bulb lights, engine unit is
internally short-circuited and should be replaced.
Refer to "Specifications” for switch setting.
4. Remove test light and reinstall wire on
engine unit.
5. If alarm buzzer sounds and/or tell-tale
lights under all conditions with engine control
switch in " O N ” position, wire leading from buzzer
or light to engine unit is shorted to ground.
6. With engine control switch in "ON"position,
and light does not come on when terminal at tem­
perature switch is shorted to ground, a break or
short in wire between engine unit and engine con­
trol switch is indicated.
7. When installing engine unit, do not use
thread compound on unit threads, as this will in­
crease electrical resistance and cause faulty re­
action.
Testing Switch Contacts
N O T E : Switch unit must be removed from en­
gine manifold in order to make this test. Before
testing unit, be sure that entire unit is pre-heated
to approximately engine temperature
Insert unit tube and lower half of body threads
in hydraulic oil, heated to a temperature 15°F. to
20 °F ., higher than unit point contact setting listed
in "Specifications." Agitate oil thoroughly (and
gently tap unit). If points contact readily, correct
working of instrument is indicated.
ENGINE THERMOSTATS
Two thermostats are installed in engine water
outlet manifold on all V-6 Gasoline Engines (fig.
3). Series 53 engines have two thermostats in­
stalled in thermostat housings at front of each
cylinder head (fig. 2).
Thermostats consist of a restriction valve
controlled by a thermostatic element. Restriction
valve cracks or just starts to open at predeter­
mined temperature and continues to open as engine
coolant temperature increases. Refer to "Coolant
Circulation" earlier in this section for operation
of engine thermostats.
N O T E : To assure proper cooling and engine
warm-up it is very important that the correct
thermostat be used. Refer to "Specifications" at
end of this section for correct thermostat appli­
cation.
T H E R M O S T A T C H E C K
If it is suspected that thermostat is not func­
tioning properly, remove thermostat assembly. If
the thermostat appears to be in good condition, the
following test should be conducted.
CHEVROLET SERIES 70 -80 H EAVY DUTY TRUCK SH O P M A N U A L