GMC 1976 ZEO 6083 Maintenance Manual page 335

6K- 4
ENGINE COOLING
COOLING SYSTEM TROUBLE DIAGNOSIS (Cont'd .)
Problem
Engine fails to reach
normal operating temper-
ature . Indicated by cool
air blown from heater .
HOT reading indicated
on temperature gauge
with no loss of coolant.
Figure 4-Cooling System Circulation
Possible Cause
Correction
Cylinder head or gaskets,
cylinder block or core
correct.
plug, heater core or
heater water valve leaking.
Thermostat stuck in closed
Replace thermostat .
position .
Thermostat stuck open or
wrong type thermostat .
type and heat range.
Coolant below add mark .
Defective engine temper-
Replace switch .
ature switch .
Repair or replace as necessary to
Install new thermostat of correct
Add coolant (50/50-coolant/water
solution).
IMPORTANT :
If the level of the coolant in the coolant recovery tank is not chang-
ing from HOT to COLD, check for a leak
in
the upper portion of the engine
cooling system .
DRAINING, FLUSHING AND REFILLING COOLING
SYSTEM
Before draining the cooling system, inspect the
system and perform any necessary service to insure
that it is clean, does not leak and is in proper working
order.
CAUTION : To avoid the danger of being
burned, and prevent loss ofcoolant, do not
remove the radiator cap while the engine
and radiator are still hot, because the cool-
ing system will blow out scalding fluid and
steam under pressure .
1 . Run engine, with radiator cap removed, until
normal operating temperature is reached . On air
conditioned models (automotive type), open water
temperature control
valve
by moving the heater tem-
perature control to maximum temperature position .
2. With engine stopped, drain radiator coolant by
opening radiator drain valve located at the lower left
corner of the radiator as shown in Figure 4. Remove
engine block drain plug on right lower side of block
if desired.
3. Close radiator drain valve, install block drain
plug, if removed, add sufficient water to fill system .