Toyota
Dodge Durango
 Service Manual
Cooling System » Diagnosis and testing
Viscous fan drive

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 excessively 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 105C (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.

    More about «Diagnosis and testing»:

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    Preliminary checks

    Electric cooling fan

    Radiator coolant flow check

    Cooling system-testing for leaks

    Viscous fan drive

    Accessory drive belt diagnosis

    Thermostat-gas engines

    Radiator cap-to-filler neck seal-pressure relief check

    Radiator cap-pressure testing

    Coolant-low level aeration

    Cooling system-deaeration

    Dodge Durango Service Manual / Cooling System / Diagnosis and testing / Viscous fan drive

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