Fan clutch issues

KATHY11458

MEMBER
1999 FORD F-350
7.3L
TURBO
4WD
AUTOMATIC
234,500 MILES

My truck is a 7.3 diesel. I am trying to determine if the fan clutch is going bad or already has. When running down the highway at about 65 to 70 mph I can hear a noise that comes and goes (almost like a fan humming noise) which is hard to hear over the diesel engine, but it definitely is there. When I go to accelerate to pass a vehicle the engine is extremely loud and does not have the power like it used to. I have looked at several video's on how to diagnose it, but I am still not sure. With the engine cold I tried turning the fan but it was extremely difficult. I barely got it to move at all. However, when the engine is running the fan is turning.
I have not noticed the engine running hot at all, but I have experienced the AC not cooling and blowing warm air.
Should I just replace the fan clutch?

1 Reply

JACOBANDNICKOLAS

MECHANIC
108,320 POSTS

Thanks for using 2CarPros.com.

When the engine is cold, the fan should turn easily. When you start the engine, there is little tension on the thermal spring. However, to confirm that it is working properly, start the engine and allow it to run for about thirty seconds. Shut the engine and then see if the fan turns easily. When the thermal spring reaches set temperatures, it will begin to tighten, resulting in the fan turning faster.

Take a look through these links:
https://www.2carpros.com/articles/how-a-clutch-fan-works

https://www.2carpros.com/articles/fan-clutch-symptoms

https://www.2carpros.com/articles/fan-clutch-removal

Here are the specific directions for testing one both at the minimum speed and maximum speed modes:

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MAXIMUM SPEED FAN CLUTCH REQUIREMENT TEST
1. Perform Steps 1 through 5 of the Fan Clutch Test-Minimum Speed Requirement.

2. NOTE: The temperature should be above 96°C (205°F) for maximum fan speed.

Block off areas on each side of the radiator in the engine compartment and the front of the radiator grille. This will raise the temperature of the air striking the fan clutch and should cause the fan blade to operate at maximum speed.
3. Place the climate control function selector switch in the MAX A/C position and the blower motor switch in the HI position.
4. Adjust the strobe to 3600 rpm.

5. WARNING: To avoid the possibility of personal injury or damage to the vehicle, do not operate the engine until the fan blade has been first examined for possible cracks and separation.

Start the engine and adjust the engine speed until the strobe light flash and the water pump pulley mark are synchronized.
6. Aim the strobe light at the fan blade retaining bolts. Adjust the strobe light until the light flash is synchronized with the marked fan blade bolt (the fan blade appears to stand still).
7. If the fan blade speed is less than 2950 rpm, replace the fan clutch.

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MINIMUM SPEED FAN CLUTCH REQUIREMENT TEST
1. Use a suitable marker to mark the water pump pulley, one of the fan blade retaining bolts and the crankshaft pulley.
2. Connect a tachometer to the engine.
3. Install a throttle adjusting tool.
4. Connect the Digital Photoelectric Tachometer.

5. WARNING: To avoid the possibility of personal injury or damage to the vehicle, do not operate the engine until the fan blade has been first examined for possible cracks and separation.

Start the engine and run it at approximately 1500 rpm until the normal operating temperature has been achieved.
6. Adjust the engine speed to 2300 rpm.
7. Operate the strobe light at 3600 rpm and aim it at the water pump pulley. Adjust the engine speed until the light flash and the water pump pulley mark are synchronized.
8. Aim the strobe light at the fan blade bolts. Adjust the strobe light until the light flash is synchronized with the marked fan blade bolt (the fan blade appears to stand still).
9. The fan blade speed must not be greater than 2000 rpm at 3000 water pump rpm.
10. Turn the engine off.
11. If the fan blade speed was greater than 2000 rpm, replace the fan clutch.
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If you find it needs replaced, here are the directions. The attached pictures correlate with these directions. The special tools required are usually available from a parts store. Most will lend them to you.

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Special Tools
Removal

CAUTION: Do not mix Standard (green) Coolant with Extended Life Coolant (orange). If this contamination occurs the service change interval on Extended Life Coolant will be reduced from 6 years/150,000 miles to 3 years/30,000 miles.
1. Remove the three bolts and position the degas bottle out of the way.
2. Squeeze the clamp, pull the hose off and position the upper radiator hose out of the way.
3. CAUTION: The large clutch assembly nut has a right-hand thread and must be rotated counterclockwise to remove it.

4. Carefully position the fan and the fan clutch into the shroud.
5. Remove the bolts, the shroud, fan and clutch.

Installation
1. Follow the removal procedure in reverse order.

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Let me know if this helps or if you have other questions.

Take care,
Joe

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