RAM 2500 Truck 4WD V10-8.0L VIN W (1997)
Viscous Fan Drive: Testing and Inspection
SPIN TEST
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.
NOTE: For the following test, the cooling system must be in good condition. It also will ensure against excessively high coolant temperature.
FUNCTION TEST
CAUTION: Be sure that there is adequate fan blade clearance before drilling.
1. Drill a 3.18 mm (1/8 inch) 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 (timing light is to be used as a strobe light).
4. Block the air flow through the radiator. Secure a sheet of plastic in front of the radiator (or air conditioner 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 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). Engagement is distinguishable by a definite
increase in fan flow noise (roaring). The timing light also will indicate an increase in the speed of the fan.
7. When the air temperature reaches 88° C (190° F), remove the plastic sheet. Fan drive disengagement 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.
CAUTION:
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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.
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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.
