Chevrolet 1977 light duty truck, Service Manual

Page: 528 / 861

G. A fter several m inutes the fan clutch should
disengage, as indicated by a reduction in fa n speed and
roar.
MAINTENANCE AND ADJUSTMENTS
C O O L A N T LEVEL
N O T E : W ith the coolant recovery system, the
coolant level is checked by observing the liquid
level in the reservoir. T h e ra d ia to r cap need not be
rem oved. The coolant level should be at the "C old
Full" m ark w hen cooling system cools and coolant
is at am b ie n t tem perature. A fter the vehicle has
been driven sufficiently to obtain n o rm al operating
te m peratures, the level should be at the "H o t Full"
mark.
T h e ra d ia to r coolant level should only be checked
w hen the engine is cool, particularly on cars equipped
with air conditioning. If the ra d ia to r cap is removed
from a hot cooling system, serious personal injury m ay
result.
Coolant level in crossflow radiators without the
coolant recovery system should be m ain tain ed three
inches below the bottom o f the filler neck w hen the
system is cold. W h e n a surge ra d ia to r supply tank is used
the coolant level should be m a in ta in e d at the one-half
full level in the supply tank. It is very im p o rtan t that the
correct fluid level be m aintained. T he sealing ability of
the ra d ia to r cap is affected w hen the cooling level is too
high.
All passenger car cooling systems are pressurized
with a 15 p o u n d pressure cap which perm its safe engine
o p e ra tio n at coolant tem p eratu res o f up to 258 °F.
W h e n the ra d ia to r cap is removed or loosened, the
system pressure drops to atmospheric, an d the heat
which had caused w ater tem p eratu re to be higher than
212°F, will be dissipated by conversion o f w ater to
steam. Inasm uch as the steam m ay form in the engine
w ater passages, it will blow coolant out o f the ra d iato r
u p p e r hose an d ta n k top, n ecessitatin g coolant
replacem ent. Engine operatin g tem peratures higher than
the norm al boiling point o f w ater are in no way
objectionable so long as the coolant level is satisfactory
w hen the engine is cool.
Upon re p eated coolant loss, the pressure ra d iato r
cap an d seat should be checked for sealing ability. Also,
the cooling system should be checked for loose hose
connections, defective hoses, gasket leaks, etc.
Cooling System Checks
1. Test for restriction in the radiator, by w arm in g
the engine up an d then turning the engine off and
feeling the radiator. The ra d ia to r should be hot along
the left side and w a rm along the right side, with an even
tem perature rise fro m right to left. Cold spots in the
ra d ia to r indicate clogged sections.
2. W a te r p u m p operatio n m ay be checked by
ru n n in g the engine while squeezing the ra d ia to r upper
hose. A pressure surge should be felt. Check for a
plugged vent-hole in pump.
NOTE: A defective head gasket may allow exhaust
gases to leak into the cooling system. This is
particularly d am a g in g to the cooling system as the
gases com bine with the w ater to form acids which
are harm fu l to the radiator and engine.
WARNING: 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.
3. To check for exhaust leaks into the cooling
system, drain coolant from the system until the coolant
level stands ju st above the top o f the cylinder head, then
disconnect the ra d iato r upp er hose and remove the
therm ostat and fan belt. Start the engine and quickly
accelerate several times. At the same time note any
appreciable w ater rise or the ap p earance o f bubbles
which are indicative o f exhaust gases leaking into the
cooling system.
Periodic M aintenance
It is the o w ner’s responsibility to keep the freeze
protection at a level com m ensurate with the area in
which the vehicle will be operated. Regardless o f
w hether freezing tem peratures are or are not expected,
cooling system protection should be m ain ta in e d at least
to -20 °F to provide adequate corrosion protection and
p roper tem perature indicating light operation. With
glycol c o n ten t
less th a n re q u ir e m e n t for -20 °F
protection, coolant boiling point is less than the
tem perature in dicating light setting. W h e n adding
solution due to loss o f coolant for any reason or in areas
where tem peratures lower than -20 °F m ay occur, a
sufficient am o u n t o f an ethylene glycol base coolant that
meets G M 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 o f w ater and a high-quality,
inhibited (perm anent-type) glycol base coolant meeting
G M
Specification 1899-M and providing freezing
protection at least to -20 °F At this time, also add G M
Cooling System In hibitor and Sealer or equivalent. In
addition, such an inhibitor and sealer should be added every
fall thereafter.
N OTE: Alcohol or methanol base coolants or plain