Dodge RAM TRUCK 1500 1995 Service Manual page 319

B R
COOLING SYSTEM SERVICE PROCEDURES 7 - 49
NOISE
It is normal for fan noise to be louder (roar­
ing) when:
• The underhood temperature is above the engage­
ment point for the viscous drive coupling. This may
occur when ambient (outside air temperature) is very
high.
• Engine loads and temperatures are high such as
when towing a trailer.
• Cool silicone fluid within the fan drive unit is be­
ing redistributed back to its normal disengaged
(warm) position. This can occur during the first 15
seconds to one minute after engine start-up on a cold
engine.
LEAIS
Viscous fan drive operation is not affected by small
oil stains near the drive bearing. If leakage appears
excessive, replace the fan drive unit.
TEST1NI
If the fan assembly free-wheels without drag (the
fan blades will revolve more than five turns when
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. It 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 in the
top center of the fan shroud.
(2) Obtain a dial thermometer with an 8 inch stem
(or equivalent). It should have a range of -18°-to-
105°C (0°-to-220° F). Insert thermometer through the
hole in 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 I S OPERATING. DO NOT STAND IN A DI­
RECT 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 2400 rpm.
Within ten minutes the air temperature (indicated on
the dial thermometer) should be up to 88° C (190° F).
Fan drive engagement should have started to occur
at between 74° to 82° C (165° to 180° F). Engage­
ment is distinguishable by a definite increase in fan
flow noise (roaring). The timing light also will indi­
cate an increase in the speed of the fan (non-diesel
only).
(7) When the air temperature reaches 88° C (190°
F), remove the plastic sheet. Fan drive disengage­
ment should have started to occur at between 57° to
79° C (135° to 175° F). A definite decrease of fan
flow noise (roaring) should be noticed. If not, replace
the defective viscous fan drive unit.
VISCOUS FAN DRIVE REMOVAL/
INSTALLATION
For removal and installation procedures, refer to
either of the previous Cooling System Fan sections.
Viscous Fan Drive Fluid Pump Out Require­
ment: After installing a new viscous fan drive, bring
the engine speed up to approximately 2000 rpm and
hold for approximately two minutes. This will ensure
proper fluid distribution within the drive.