Chevrolet 70 1969 Series, Shop Manual

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ENGINE C O O LIN G SYSTEM 6K-3
operating temperature, thermostats begin to open.
As thermostats open, a gradual increasing volume
of coolant flows through radiator, while a gradual
decreasing volume flows through the by-pass sys­
tem. Thermostats regulate flow to maintain an
operating temperature within the specified limits.
INSPECTION OF SYSTEM
Although action of the cooling system controls
the operating temperature of the engine, improper
ignition timing (gasoline engines) or improper or
insufficient lubricating oil in the engine crankcase
may cause the engine to overheat, even though the
cooling system is functioning properly. These
items should also be checked for cause of improper
cooling.
Cooling systems must be kept air-tight. As
the pressure in the system raises the boiling point
of the coolant, any air leak would lower boiling
point and result in loss of coolant. Check radiator
cap seal and all radiator connections. Entire cool­
ing system can be checked for leaks in castings,
connection hoses, gaskets, pressure valves, and
filler cap using a conventional cooling system test­
ing kit which can usuallv be obtained locally.
C A U T IO N : When the engine is at normal oper­
ating temperature or above, the internal pressure
built up in the cooling system will blow out scalding
fluid and vapors if the radiator cap is suddenly re­
moved. To prevent loss of coolant and to avoid the
danger of being burned, the coolant level should be
checked or coolant added only when the engine is
cool. If the cap must be removed when the engine
is hot, place a cloth over the cap and rotate the cap
slowly counterclockwise to first stop and allow
pressure to escape completely. Then turn cap again
slowly counterclockwise to remove.
D R A IN IN G C O O LIN G SYSTEM
1. On tilt cab models, place heater tempera­
ture control in " H E A T " position.
2. Remove radiator filler cap.
3. Remove plug or open drain cock at bottom
of radiator core.
4. Open petcock or remove drain plug at each
side of cylinder block.
5. Remove drain plug from bottom of engine
oil cooler (if equipped).
6. Remove drain plug from bottom of cooling
system filter assembly (if equipped).
7. If vehicle is equipped with a water cooled
air compressor, disconnect air compressor cool­
ant hose from side of cylinder block.
FILLING C O O LIN G SYSTEM
When cold water is poured into the radiator,
the thermostats will close even though the engine
is warm. This action may trap air in cylinder
block and head passages. The trapped air will leak
through the thermostat vents, thereby lowering the
water level.
N O T E : Before filling, flush out the cooling
system with plain water.
1. On tilt cab models, the heater control valve
must be in wide open " H E A T " position before
filling the cooling system. This will prevent air
from being trapped in heater and lines.
2. When checking coolant level, remove rad­
iator cap S L O W L Y (if engine is hot). No additional
water is required if water is visible in filler neck
or at bottom of filler tube.
3. With all drains closed, add coolant until
visible in filler neck or at bottom of filler tube.
4. Add more coolant slowly until no air
bubbles can be seen; then, run engine for a few
minutes to expel air. Add coolant as necessary to
bring to proper level.
N O T E : The coolant level should be approxi­
mately one-inch below bottom of filler neck when
engine is hot. If engine is cold, the coolant level
should be two to three inches below bottom of
filler neck.
5. If vehicle is equipped with a water-cooled
air compressor, vent air from compressor cool­
ing cavities and connecting lines by loosening
small hex plug at high side of compressor.
6. Do not overfill and do not pour cold water
into radiator while engine is hot. Wait until boiling
ceases, then add water slowly while engine is
idling. Install radiator cap firmly.
CLEANING SYSTEM
Unless water in cooling system is treated with
a corrosion preventive, rust and scale may event­
ually clog water passages in radiator and water
jackets. This condition is aggravated in some lo­
calities by the formation of insoluble salts from
water used.
Cleaning solutions, commercially available,
will successfully clean cooling systems of rust,
scale, sludge, and grease when used as directed
by the manufacturers. However, if radiator is
clogged with insoluble scale formations, reliable
radiator service stations in the various localities
are best equipped to remove such formations.
Chevrolet Cooling System Cleaner or other
commercial cleaning solutions are especially
effective in removing rust, scale, and corrosion
from the radiator and engine water passages. Use
cleaner only as directed on label. Particularly at
winter check-up, preferably before and after using
anti-freeze solutions, radiator and entire system
should be cleaned with a recommended cleaning
solution as follows:
CHEVROLET SERIES 70-80 H EAVY DUTY TRUCK SH O P M A N U A L