Chevrolet Light Duty Truck 1973 Service Manual page 418

6 K - 8 E N G IN E C O O L IN G
Periodic Maintenance
It is the owner's responsibility to keep the freeze
protection at a level commensurate with the area in
which the vehicle will be operated. Regardless of climate,
system protection should be maintained at least to -20°F.,
to provide adequate corrosion protection. When adding
solution due to loss of coolant for any reason or in areas
where temperatures lower than -20°F. may occur, a
sufficient amount of an ethylene glycol base coolant that
meets GM Specification 1899-M should be used.
Every two years the cooling system should be serviced by
flushing with plain water, then completely refilled with a
fresh solution of water and high-quality inhibited
(permanent-type) glycol base coolant meeting GM
Specification 1899-M, and providing freezing protection
at least to -20°F. At this time, also add GM Cooling
System Inhibitor and Sealer or equivalent. In Addition,
Cooling System Inhibitor and Sealer should be added
every fall thereafter. GM Cooling System Inhibitor
retards the formation of rust or scale and is compatible
with aluminum components.
NOTE: Alcohol or methanol base coolants or
plain water are not recommended for your
cooling system at any time.
Two common causes of corrosion are: (1) air suction—Air
may be drawn into the system due to low liquid level in
the radiator, leaky water pump or loose hose connec­
tions; (2) exhaust gas leakage— Exhaust gas may be
blown into the cooling system past the cylinder head
gasket or through cracks in the cylinder head and block.
Cleaning
A good cleaning solution should be used to loosen the
rust and scale before reverse flushing the cooling system.
There are a number of cleaning solutions available and
the manufacturer's instructions with the particular
cleaner being used should always be followed.
An excellent preparation to use for this purpose is GM
Cooling System Cleaner or its equivalent. The following
directions for cleaning the system applies only when this
type cleaner is used.
If you siphon coolant from the
WARNING:
radiator, do not use mouth to start siphoning
action. The coolant solution is POISONOUS
and can cause death or serious illness if
swallowed.
1. Siphon coolant from the cooling system, including
the cylinder block.
2. Remove thermostat and replace thermostat housing.
3. Add the liquid portion (No. 1) of the cooling system
cleaner.
4. Fill the cooling system with water to a level of
about 3 inches below the top of the overflow pipe.
5. Cover the radiator and run the engine at moderate
speed until engine coolant temperature reaches 180
degrees.
6. Remove cover from radiator and continue to run
the engine for 20 minutes. Avoid boiling.
7. While the engine is still running, add the powder
portion (No. 2) of the cooling system cleaner and
continue to run the engine for 10 minutes.
BE CAREFUL NOT TO SCALD
WARNING:
YOUR HANDS.
8. At the end of this time, stop the engine, wait a few
minutes and then open the engine block drain
cocks. Also, remove lower hose connection.
NOTE: Dirt and bugs may be cleaned out of
the radiator air passages by blowing out with
air pressure from the back of the core. Do
not bend radiator fins.
Reverse Flushing
Reverse flushing should always be accomplished after
the system is thoroughly cleaned as outlined above.
Flushing is accomplished through the system in a
direction opposite to the normal flow. This action causes
the water to get behind the corrosion deposits and force
them out.
Radiator
1. Remove the radiator upper and lower hoses and
replace the radiator cap.
2. Attach a lead-away hose at the top of the radiator.
3. Attach a new piece of hose to the radiator outlet
connection and insert the flushing gun in this hose.
4. Connect the water hose of the flushing gun to a
water outlet and the air hose to an air line.
5. Turn on the water and when the radiator is full,
turn on the air in short blasts, allowing the radiator
to fill between blasts of air.
Apply air gradually as a clogged
CAUTION:
radiator will stand only a limited pressure.
6. Continue this flushing until the water from the
lead-away hose runs clear.
Cylinder Block and Cylinder Head
1. With the thermostat removed, attach a lead-away
hose to the water pump inlet and a length of new
hose to the water outlet connection at the top of the
engine.
NOTE: Disconnect the heater hose and cap
connections at engine when reverse flushing
engine.
2. Insert the flushing gun in the new hose.
3. Turn on the water and when the engine water
jacket is full, turn on the air in short blasts.
LIGHT DUTY TRUCK SERVICE MANUAL