Dodge ram truck 3500 1996 Service Manual page 313

B R COOLING SYSTEM 7 - 29
DIAGNOSIS AND TESTING
{ C o n t i n u e d )
spun by hand), replace the fan drive. This spin test
must be performed when the engine is cool.
For the following test, the cooling system must be
in good condition. I t also will ensure against exces­
sively high coolant temperature.
WARNING; BE SURE THAT THERE IS ADEQUATE
FAN BLADE CLEARANCE BEFORE DRILLING.
(1) Drill a 3.18-mm (1/8-in) diameter hole i n the
top center of the fan shroud.
(2) Obtain a dial thermometer with an 8 inch stem
(or equivalent). I t should have a range of -18°-to-
1 0 5 ° C
(0°-to-220°
F). Insert thermometer through the
hole i n the shroud. Be sure that there is adequate
clearance from the fan blades.
(3) Connect a tachometer and an engine ignition
timing light. The timing light is to be used as a
strobe light. This step cannot be used on the diesel
engine.
(4) Block the air flow through the radiator. Secure
a sheet of plastic in front of the radiator (or air con­
ditioner condenser). Use tape at the top to secure the
plastic and be sure that the air flow is blocked.
(5) Be sure that the air conditioner (if equipped) is
turned off.
WARNING: USE EXTREME CAUTION WHEN THE
ENGINE IS OPERATING- DO NOT STAND IN A
DIRECT LINE WITH THE FAN. DO NOT PUT YOUR
HANDS NEAR THE PULLEYS, BELTS OR FAN. DO
NOT WEAR LOOSE CLOTHING.
( 6 )
Start the engine and operate at
2 4 0 0
rpm.
Within ten minutes the air temperature (indicated on
the dial thermometer) should be up to 8 8 ° C ( 1 9 0 ° F).
Fan drive engagement should have started to occur
at between 7 4 ° to 8 2 ° C ( 1 6 5 ° to 1 8 0 ° F). Engage­
ment is distinguishable by a definite increase i n fan
flow noise (roaring). The timing light also will indi­
cate an increase i n the speed of the fan (non-diesel
only).
( 7 ) When the air temperature reaches 8 8 ° C ( 1 9 0 °
F), remove the plastic sheet. Fan drive disengage­
ment should have started to occur at between 5 7 ° to
7 9 ° C ( 1 3 5 ° to 1 7 5 ° F). A definite decrease of fan
flow noise (roaring) should be noticed. I f not, replace
the defective viscous fan drive unit.
CAUTION: Some engines equipped with serpentine
drive belts have reverse rotating fans and viscous
fan drives. They are marked with the word
REVERSE to designate their usage. Installation of
the wrong fan or viscous fan drive can result in
engine overheating.
CAUTION: If the viscous fan drive Is replaced
because of mechanical . damage, the cooling fan
blades should also be inspected. Inspect for fatigue
cracks, loose blades, or loose rivets that could
have resulted from excessive vibration. Replace fan
blade assembly if any of these conditions are
found. Also inspect water pump bearing and shaft
assembly for any related damage due to a viscous
fan drive malfunction.
SERPENTINE DRIVE BELT DIAGNOSIS—ALL
ENGINES
When diagnosing serpentine drive belts, small
cracks that run across ribbed surface of belt from rib
to rib (Fig. 3 4 ) , are considered normal. These are not
a reason to replace belt. However, cracks running
along a rib (not across) are not normal. Any belt
with cracks running along a rib must be replaced
(Fig. 3 4 ) . Also replace belt i f i t has excessive wear,
frayed cords or severe glazing.
Refer to the Serpentine Drive Belt Diagnosis chart
for further belt diagnosis. Also refer to Automatic
Belt Tensioner proceeding in this group.
NORMAL CRACKS
BELT OK
NOT NORMAL CRACKS
REPLACE BELT
J9007-44
* Fig. 34 Serpentine Accessory Drive Beit Wear
Patterns