GMC 4000 Series Service Manual page 546

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Subject
Description
Maintenance
Radiator Mountings
Radiator R e p la ce m en t..................................................
Radiator Filler Cap
Radiator Surge Tank
Engine Coolant
manual for information relative to engine coolant circula­
tion, system capacities, temperature indicators, thermostats
water filters, and fan belts. Information on replacement of
radiator shell and front end sheet metal is provided in
SHEET METAL (SEC. 11) of this manual.
DESCRIPTION
Pressurized cooling with regulated coolant
flow is standard on all models. Use of pressurized
system allows increased coolant operating temper­
atures for improved efficiency, extended engine
life, and minimum coolant lo ss. Pressure valve in
radiator filler cap is used to maintain specified
pressure within cooling system . Temperature of
coolant is regulated by thermostat control in engine.
Radiator assem blies are engineered with op­
timum frontal core area and maximum heat trans­
fer characteristics. Some radiator assem blies are
fitted with a shroud designed to assist fan in di­
recting air flow through radiator core and also
serve as a fan guard. For continuous heavy-duty
applications, radiator assem blies with increased
cooling capacity are available as optional equipment.
Provision for coolant expansion is achieved by
maintaining an air reservoir in upper radiator tank
or surge tank. This retards coolant overflow re­
ducing necessity of frequent refills.
Surplus coolant is released through filler cap
pressure valve and neck vent to which is connected
an overflow tube. Purpose of overflow tube is to
allow excess coolant to be released beneath vehicle.
Pressure in cooling system is maintained by
use of radiator cap equipped with two valves; one
which relieves excessive pressure in system and
another which admits outside air to compensate
for coolant contraction after engine is stopped.
Radiator caps are provided with pressure ratings
of 9 or 13 pounds per square inch. Coolant boiling
point increases approximately 3 degrees for each
additional pound of pressure. Refer to "Specifica­
tions" at end of this section for correct replace­
ment radiator filler cap.
G M C S E R V I C E M A N U A L
SECTION 13
A S u A ae ^ la n k
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NOTE: Refer to ENGINE COOLING (SEC. 6K) of this
Page No.
535
535
536
536
537
538
538
MAINTENANCE
At regular intervals, cooling system compon­
ents should be inspected to determine if service
is required. Regular systematic checks will reveal
faulty condition of various units and indicate nec­
essity of servicing or replacement of such com­
ponents before failure occurs. Suggested checks
are:
1. Frequently check coolant level. If low, add
recommended coolant as required.
2. Check hose connections and tighten clamps
if seeping is evident. Cracked, stripped, or cor­
roded clamps should be replaced.
3. Inspect radiator hoses for spongy or check­
ed appearance. Deteriorated hoses should be re­
placed before bursting occurs which would result
in coolant loss and could cause extensive engine
damage due to overheating.
3. Check radiator core for leaks and for ac­
cumulation of dirt which obstructs air passage and
reduces effective heat transfer.
4. Inspect resilient radiator mountings for
deterioration and replace as required. Keep mount­
ing bolts tight to prevent core damage due to road
shocks and vibration. Check side flanges and sup­
port braces for evidence of metal damage if mount­
ing bolts are missing, loose, or stripped.
5. Inspect for proper clearance between fan
blades, radiator core, and shroud (if equipped).
Check fan attaching bolts for tightness and observe
alignment of fan blades in relation to each other.
Replace fan if any blade is bent. Distance between
blades and shroud should be equal around entire
perimeter of shroud. If adjustment is required,
shroud attaching bolts may be loosened and shroud
shifted as necessary to provide proper clearance.
Sec. 13
Page 535