Chevrolet 1977 light duty truck, Service Manual

Page: 529 / 861

w ater are not recom m ended for your engine at any
time.
Two com m on causes o f corrosion are: (1) air
suction—Air m ay be drawn into the system due to low
liquid level in the radiator, leaky water pu m p or loose
hose connections, defective pressure cap or leaky
overflow hose connection to ra d ia to r on recovery bottle;
(2) exhaust gas leakage—Exhaust gas m ay 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 n u m b e r o f cleaning solutions
available and the m a n u f a c tu r e r ’s instructions with the
p articu lar cleaner being used should always be followed.
An excellent p re p a ra tio n to use for this purpose is
G M Cooling System Cleaner or its equivalent. The
following directions for cleaning the system applies only
w hen this type cleaner is used.
W ARNING : If you siphon coolant from the
radiator, do not use mouth to start siphoning
action. The coolant solution is POISONOUS
and can cause death or serious illness if
swallowed.
1. D ra in coolant from the cooling system, includ­
ing the cylinder block.
N O T E : The V8 cylinder block drain plugs are
located on both sides o f the block about halfway
back and on the lower edge n ear the oil pan rail.
T h e 6-cylinder block d ra in is located on the left
side o f the engine at about centerline o f the block
a n d adjacent to the flywheel housing.
2. Remove therm ostat and replace thermostat
housing.
3. A dd the liquid portion (No. 1) o f the cooling
system cleaner.
4. Fill the cooling system with w ater to a level o f
about 3 inches below the top o f the overflow pipe.
5. Cover the ra d ia to r and run the engine at
m o d erate speed until engine coolant tem perature reaches
180 degrees.
6. Remove cover from ra d iato r and continue to
ru n the engine for 20 minutes. Avoid boiling.
7. W hile the engine is still running, add the
powder portion (No. 2) o f the cooling system cleaner and
continue to run the engine for 10 minutes.
W ARNING : Be careful not to scald your
hands.
8. At the end o f this time, stop the engine, wait a
few minutes and then open the d ra in cocks.
NOTE: Dirt and bugs may be cleaned out o f the
rad iato r air passages by blowing out with air
pressure from the back o f the core. Do not bend
rad iato r 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 norm al flow. This action causes
the w ater to get behind the corrosion deposits and force
them out.
Radiator
1. Remove the ra d ia to r upper and lower hoses and
replace the ra d ia to r cap.
2. Attach a lead-away hose at the top o f the
radiator.
3. Attach a new piece o f hose to the ra d ia to r outlet
connection and insert the flushing gun in this hose.
4. Connect the w ater hose o f the flushing gun to a
w ater outlet and the air hose to an air line.
CAUTION: A pply air gradually as a clogged
radiator will sta n d only 20 p.s.i. pressure.
5. T urn on the w ater and when the ra d ia to r is full,
turn on the air in short blasts, allowing the ra d ia to r to fill
between blasts o f air.
6. C ontinue this flushing until the w ater from the
lead-away hose runs clear.
Cylinder Block and Cylinder Head
1. W ith the therm ostat removed, attach a lead-
away hose to the w ater p u m p inlet and a length o f new
hose to the w ater outlet connection at the top o f the
engine.
NOTE: Disconnect the heater hose and cap
connections at engine w hen reverse flushing
engine.
2. Insert the flushing gun in the new hose.