GM 6.5L V8 – Cooling Fan Assembly

The cooling fan assembly, along with the water pump pulley, mounts to the water pump with studs and nuts. The accessory drive belt operation of the water pump also rotates the shaft and driving member of the fan clutch at all times. An aluminum housing has the fan blade assembly bolted to it and is the driven member of the fan clutch.

The operation of the fan occurs when the driving and driven members of the clutch are held together hydraulically by silicone fluid (see Figure 4-13, view A). A bimetallic coil controls the flow of silicone fluid from a reservoir (through a pump plate) to the area between the driving and driven members of the fan clutch (see Figure 4-13, view B). As the two members attempt to shear the silicone fluid, a coupling action takes place.

When the temperature of the air flowing through the radiator is below 165° F (74° C), the bimetallic coil operation of the pump plate prevents the silicone fluid from moving to the area between the drive and driven members of the fan clutch (see Figure 4-14, view A). Even though the accessory drive belt is rotating, it is not rotating the fan blades with force.

When the temperature of the air flowing through the radiator is above 165° F (74° C), the bimetallic coil operation of the pump plate allows the silicone fluid to move into the area between the drive and driven members of the fan clutch (see Figure 4-14, view B). Now the accessory drive belt rotates the fan blades with force.

The following diagnosis hints relate to cooling fan operation:
Condition #1: Noise
Cause: A. Clutch distributing silicone fluid immediately after engine start-up
B. Clutch fully applied to provide maximum cooling
Correction: A and B. None, since the conditions are normal.

Condition #2: Looseness
Cause: Approximately 1/4-inch lateral movement at the fan blade tip (related to the fan clutch bearing design)
Correction: None, since the condition is normal.

Condition #3: Leakage
Cause: Small silicone fluid leakage in the bearing area
Correction: None, since the condition is normal.

Condition #4: Engine overheating
Cause: Incorrect fan clutch operation
Correction: Follow this diagnostic sequence:
1. Allow the engine to cool for complete fan clutch release.
2. Spin the fan/clutch assembly to check for slight drag.
• Replace the fan clutch if it spins for more than five revolutions.
• Replace the fan blade assembly if any blades are bent.
3. Mount a thermometer in the airflow path (on the fan shroud) between the radiator and fan.
4. Start the engine and operate it at 2,000 rpm (A/C on) with the radiator grille covered.
5. Observe the thermometer reading when the fan clutch applies.
• Noise indicates fan clutch apply, as well as a temperature drop of 5° to 15° F (3° to 9° C).
• Replace the fan clutch if no clutch apply occurs.
• Replace the fan clutch if the temperature of clutch apply is not 150° to 195° F (66° to 91 ° C).
6. Uncover the radiator grille and run the engine at 1,500 rpm for cooling.
7. After several minutes of engine operation, check that the fan clutch releases.
• Replace the fan clutch if no clutch relase occurs.

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