Chevrolet 10 1971 Series, Руководство по обслуживанию шасси

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ENGINE COOLING 6K-2
Water pump components are not serviced separately; For radiator service refer to Section 13 of this manual,
therefore, in the event of water pump failure, it will be Radiator fan shroud replacement is covered in Section 11
necessary to replace the complete assembly - removal of this manual,
and installation procedures are covered in this section.
M AINTENANCE A N D ADJUSTMENTS
Coolant Level
The radiator coolant level should only be checked
when the engine is cool, particularly on trucks equipped
with air conditioning. If the radiator cap is removed
from a hot cooling system, serious personal injury may
result.
The cooling system fluid level in downflow radiator
should be maintained one inch below the bottom of the
filler neck of the radiator when cooling system is cold.
Coolant level in crossflow radiators should be maintained
three inches below the bottom of the filler neck when the
system is cold. (Note coolant level arrow on rear of
radiator outlet tank.) It is very important that the
correct fluid level be maintained. The sealing ability of
the radiator cap is affected when the cooling level is too
high.
All truck cooling systems are pressurized with a 15
lb„ pressure cap which permits safe engine operation at
cooling temperatures of up to 256°F. with a 33% glycol
solution.
When the radiator cap is removed or loosened, the
system pressure drops to atmospheric, and the heat
which had caused water temperature to be higher than
212° F, will be dissipated by conversion of water to
steam. Inasmuch as the steam may form in the engine
water passages, it will blow coolant out of the radiator
upper hose and top tank, necessitating coolant replace­
ment. Engine operating temperatures higher than the
normal boiling point of water are in no way objectionable
so long as the coolant level is satisfactory when the
engine is cool.
Upon repeated coolant loss, the pressure radiator cap
and seat should be checked for sealing ability. Also, the
cooling system should be checked for loose hose connec­
tions, defective hoses, gasket leaks, etc.
Coolant System Checks
1. 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 at the top
(along the left side on crossflow radiators) and warm
at the bottom (along the right side on crossflow radi­
ators), with an even temperature rise from bottom
to top (right to left on crossflow radiators). Cold
spots in the radiator indicate clogged sections.
2. Water pump operation may be checked by running the
engine while squeezing the upper radiator hose. A
pressure surge should be felt. Check for a plugged
vent-hole in pump.
NOTE:
A defective head gasket may allow ex­
haust gases to leak into the cooling system.
This is particularly damaging to the cooling
system as the gases combine with the water to
form acids which are harmful to both the radia­
tor and engine.
3. 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 upper radiator hose and remove the thermostat
and fan belt. Start the engine and quickly accelerate
several times. At the same time note any appreci­
able water rise or the appearance of bubbles which
are indicative of exhaust gases leaking into the cool­
ing system.
Periodic Maintenance
It is the owner's responsibility to keep the freeze pro­
tection 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 0°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 Speci­
fication 1899-M, and providing freezing protection at
least to 0°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 alumi­
num 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 sys­
tem. 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.
1. Drain the cooling system including the cylinder block,
and then close drain plugs.
2. Remove thermostat and replace thermostat housing.
3. Add the liquid portion (No. 1) of the cooling system
cleaner.
10-30 CHEVROLET TRUCK SERVICE MANUAL