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66-6
1977 PONTIAC SERVICE MANUAL
TROUBLE DIAGNOSIS
The following diagnostic information covers
common problems and possible causes. When the
proper diagnosis is made the problem should be
corrected by part replacement, adjustment, or
repair as required. Refer to the appropriate section
of the service manual for these procedures.
FAN CLUTCH DIAGNOSTIC
PROCEDURE
1. NOISE
Fan noise is sometimes evident under the following
normal conditions:
a. When clutch is engaged for maximum cooling.
b. During first few minutes after start-up until the clutch
can re-distribute the silicone fluid back to its normal
disengaged operating condition after overnight settling.
However, fan noise or an excessive roar will generally
occur continuously under all high engine speed conditions
(2500 r.p.m. and up) if the clutch assembly is locked up due
to an internal failure. If the fan cannot be rotated by hand
or there is a rough grating feel as the fan is turned, the clutch
should be replaced.
2. LOOSENESS
Under various temperature conditions, there is a visible
lateral movement that can be observed at the tip of the fan
blade. This is a normal condition due to the type of bearing
used. Approximately 1 /4" maximum lateral movement
measured at the fan tip is allowable. This is not cause for
replacement.
3. SILICONE FLUID LEAK
The operation of the unit is generally not affected by
small fluid leaks which may occur in the area around the
bearing assembly. However, if the degree of leakage appears
excessive, proceed to item 4.
4. ENGINE OVERHEATING
a. Start with a cool engine to insure complete fan clutch
disengagement.
b. If the fan and clutch assembly free-wheels with no
drag (revolves over 5 times when spun by hand), the clutch
should be replaced. If clutch performs properly with a slight
drag go to step c.
NOTE: Testing a fan clutch by holding the small hub
with one hand and rotating the aluminum housing in a
clockwise/counterclockwise
motion will cause the
clutch to free-wheel, which is a normal condition when
operated in this manner. This should not be considered
a test by which replacement is determined.
NOTE: pointer movement for each 10" (6°C.) over
180°F. (82°C.).
Position thermometer so that the thermomoeter sensor
is centered in the space between the fan blades and radiator.
This can be achieved by inserting the sensor through one of
the existing holes in the fan shroud or fan guard, or by placing
between the radiator and the shroud. On some models, it may
be necessary to drill a 3/16" hole in the fan shroud to insert
J 6742-0 1.
CAUTI 0 N: Check for adequate clearance
between h n blades and thermometer sensor before
starting engine.
d. Cover radiator grille sufficiently to induce a high
engine temperature. Start engine and turn on A/C if
equipped. Maintain a position in front of the vehicle to
observe the thermometer reading while engine is running at
approximately 2000 r.p.m. Use tachometer if available.
e. Observe thermometer reading when clutch engages.
It will take approximately 5 to 10 minutes for the temperature
to become high enough to allow engagement of the fan clutch.
This will be indicated bv an increase or roar in fan air noise
and by a drop in the thermometer reading of approximately
515°F. (3-8°C.) If the clutch did not engage between 150-
190°F. (65-88"C.), the unit should be replaced.
NOTE: Be sure fan clutch was disengaged at beginning
of test.
If no sharp increase in fan noise or temperature drop was
observed and the fan noise level was constantly high from
start of test to 190°F. (88°C.) the unit should be replaced.
CAUTION: Do not continue test past
a
thermometer reading o f 190°F: (88°C.) to prevent
engine overheating.
f. As soon as the clutch engages, remove the radiator
grille cover and turn off the A/C to assist in engine cooling.
The engine should be run at approximately 1500 r.p.m.
g. After several m i h t e s the fan clutch should disengage,
as indicated by a reduction in fan speed and roar.
c. Use dial type thermometer J 23640, or similar type.
NOTE: J 23640 reads to 220" F. (1 15"C.), therefore,
allow approximately 3/16" pointer movement for each
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