Chevrolet Light Duty Truck 1973 Service Manual page 421

1. Siphon coolant from the radiator and break loose
the fan pulley bolts.
2. Disconnect heater hose, radiator lower hose and by­
pass hose (as required) at water pump.
3. Loosen Delcotron and remove fan belt then remove
fan bolts, fan and pulley.
I f a fan blade is bent or damaged
CAUTION:
in any way, no attempt should be made to
repair and reuse the damaged part. A bent or
damaged fan assembly should always be
replaced with a new fan assembly.
It is essential that fan assemblies remain in proper
balance and proper balance cannot be assured once
a fan assembly has been bent or damaged. A fan
assembly that is not in proper balance could fail and
fly apart during subsequent use creating an
extremely dangerous condition.
NOTE: Thermostatic fan clutches must be
kept in an "in-car" position. When removed
from the car the assembly should be
supported so that the clutch disc remains in a
If the radiator is filled too full when cold, expansion
when hot will overfill the radiator and coolant will be lost
through the overflow pipe. Adding unnecessary water
will weaken the anti-freeze solution and raise the
temperature at which freezing may occur.
If the cooling system requires frequent addition of water
in order to maintain the proper level in the radiator,
check all units and connections in the cooling system for
evidence of leakage. Inspection should be made with
cooling system cold. Small leaks which may show
dampness or dripping can easily escape detection when
the engine is hot, due to the rapid evaporation of
coolant. Tell-tale stains of grayish white or rusty color, or
dye stains from anti-freeze, at joints in cooling system
are almost always sure signs of small leaks even though
there appears to be no damage.
Air or gas entrained in the cooling system may raise the
level in radiator and cause loss of coolant through the
overflow pipe. Air may be drawn into the cooling system
through leakage at the water pump seal. Gas may be
forced into the cooling system through leakage at the
cylinder head gasket even though the leakage is not
sufficient to allow water to enter the combustion
chamber.
COOLING SYSTEM CHECKS
To check for exhaust leaks into the cooling system, drain
the system until the water level stands just above the top
of the cylinder head, then disconnect the radiator upper
hose and remove the thermostat and fan belt. Start the
engine and quickly accelerate several times. At the same
vertical plane to prevent silicone fluid
leakage.
4. Remove pump to cylinder block bolts and remove
pump and old gasket from engine.
NOTE: On in line engines, pull the pump
straight out of the block first, to avoid
damage to impeller.
Installation
1. Install pump assembly on cylinder block then, using
a new, sealer coated, pump-to-block gasket tighten
bolts securely.
2. Install pump pulley and fan on pump hub and
tighten bolts securely.
NOTE: A guide stud (5/16"-24 x 1" bolt with
the head removed) installed in one hole of
the fan will aid in aligning hub, pulley and
fan. Remove stud after starting the remain­
ing three bolts.
3. Connect hoses and fill cooling system.
4. Install fan belt and adjust as previously outlined.
5. Start engine and check for leaks.
D IA G N O S IS
time note any appreciable water rise or the appearance
of bubbles which are indicative of exhaust gases leaking
into the cooling system.
Water pump operation may be checked by running the
engine while squeezing the radiator upper hose. A
pressure surge should be felt. Check for a plugged vent­
hole in pump.
Test for restriction in the radiator, by warming the
engine up and then turning the engine off and feeling
the radiator. The radiator should be hot along the left
side and warm along the right side, with an even
temperature rise from right to left. Cold spots in the
radiator indicate clogged sections.
An operational check of the thermostat can be made by
hanging thermostat on a hook in a 33% glycol solution
25° above the temperature stamped on the thermostat
valve. Submerge the valve completely and igitate the
solution thoroughly. Under this condition the valve
should open. Remove the thermostat and place in a 33%
glycol solution 10° below temperature indicated on the
valve. With valve completely submerged and water
agitated thoroughly, the valve should close completely.
Coolant Loss
1. Make sure owner is not trying to keep radiator
filled to top, and is not filling while cold. The
expansion and contraction of water during opera­
tion will cause level to drop below top of filler neck.
E N G IN E C O O L I N G 6K -1 1
LIGHT DUTY TRUCK SERVICE MANUAL