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Old 06-04-2019, 08:57 PM   #21
Cheyenne
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Default Re: Viscous Fan Clutch Replacment

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Originally Posted by autostaretx View Post
The original fan looks slightly asymmetric ... the blades don't appear to be spaced evenly.
(but it could simply be the slight angle of the photo)

I wonder if that's to avoid setting up some resonances?

--dick
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Old 06-04-2019, 09:20 PM   #22
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Default Re: Viscous Fan Clutch Replacment

There in undoubtedly a speed where the fan blades start to resonate due to shed vortices. Given the large rpm range the fan operates over, its impossible to tune the blade length and chord width to eliminate all the possible vibration modes. To avoid fatigue failure the resonant frequencies need to be canceled at least to the 1st order. This also makes the fan quieter. One method to accomplish this is by have a decreasing blade spacing in several successive blades (2-3 groups usually). As it is still symmetric, the balance is not affected. The different spacing means the shed vortices impact the trailing blades at slightly different rates preventing them from stacking from one blade to the next.

For fixed speed or narrow speed fans this is less of an issue. blowers or fans where both ends of the blade are supported have less of an issue with this.
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Old 06-05-2019, 12:18 AM   #23
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Default Re: Viscous Fan Clutch Replacment

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Originally Posted by Midwestdrifter View Post
There in undoubtedly a speed where the fan blades start to resonate due to shed vortices. Given the large rpm range the fan operates over, its impossible to tune the blade length and chord width to eliminate all the possible vibration modes. To avoid fatigue failure the resonant frequencies need to be canceled at least to the 1st order. This also makes the fan quieter. One method to accomplish this is by have a decreasing blade spacing in several successive blades (2-3 groups usually). As it is still symmetric, the balance is not affected. The different spacing means the shed vortices impact the trailing blades at slightly different rates preventing them from stacking from one blade to the next.

For fixed speed or narrow speed fans this is less of an issue. blowers or fans where both ends of the blade are supported have less of an issue with this.
That can clearly be seen on both fans. The older blade has 7 blades, spaced differently. The new fan has 9, also spaced differently. I don't see a clear line of symmetry, but I would guess they are arranged such that the balance is not affected. The new fan is less noisy than the old, but it also may be that the clutch is not fully engaging. Coolant temps with the old hovered around 180-190. With the new, they are in the 190-200 range.

Regards,

Mark
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Old 06-05-2019, 01:12 PM   #24
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Default Re: Viscous Fan Clutch Replacment

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Originally Posted by marklg View Post
... The new fan is less noisy than the old, but it also may be that the clutch is not fully engaging. Coolant temps with the old hovered around 180-190. With the new, they are in the 190-200 range.

Regards,

Mark
I was surprised when the operating temperatures on the 2004 actually increased a bit with the new clutch. The new clutch roars more upon a morning cold start than did the replaced clutch. (Viscous fluid pools overnight.)

My typical low temperature rose, the high peaks came down after the new clutch. My theory for the unexpected slight rise in lower operating temperature is that my 2004 clutch was stuck in some mid range operating condition. It never locked up completely or disengaged, but did kinda work in a limited range. When the engine is hot the thermostat opens completely. It takes a bit of a temperature drop for it to cycle back. At that time it is the fan speed which becomes an important factor for trimming the temperatures to design, not the thermostat. With the 2004 fan never properly disengaging the engine was being supercooled at times.

vic
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Old 06-05-2019, 02:52 PM   #25
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Default Re: Viscous Fan Clutch Replacment

Quote:
Originally Posted by Aqua Puttana View Post
I was surprised when the operating temperatures on the 2004 actually increased a bit with the new clutch. The new clutch roars more upon a morning cold start than did the replaced clutch. (Viscous fluid pools overnight.)

My typical low temperature rose, the high peaks came down after the new clutch. My theory for the unexpected slight rise in lower operating temperature is that my 2004 clutch was stuck in some mid range operating condition. It never locked up completely or disengaged, but did kinda work in a limited range. When the engine is hot the thermostat opens completely. It takes a bit of a temperature drop for it to cycle back. At that time it is the fan speed which becomes an important factor for trimming the temperatures to design, not the thermostat. With the 2004 fan never properly disengaging the engine was being supercooled at times.

vic
The knockoff clutch failed in the middle of nowhere, in the desert, driving along when suddenly the engine noise increased to a roar. I guess it was a good thing it failed completely on. The rise in temperature after replacement was as expected. We will have to see what the temp gets to climbing hills at high ambient temperature.

The first clutch, before the knockoff, had failed off, so the electric fan was running all the time, and the temp rose drastically on hills. So, at least I have data points for fully off, fully on, and normal operation.

Regards,

Mark
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Old 06-08-2019, 11:35 PM   #26
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Default Re: Viscous Fan Clutch Replacment

With a new, good Febi Bilstein fan and clutch in my 2006 T1N, with ambient temperatures between 71 and 98 F, varying speeds, uphill and down, I saw a range of coolant temperatures between 185 and 223 F. Average is about 200F.

Regards,

Mark
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Old 06-16-2019, 06:21 AM   #27
Nautamaran
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Default Re: Viscous Fan Clutch Replacment

Quote:
Originally Posted by marklg View Post
With a new, good Febi Bilstein fan and clutch in my 2006 T1N, with ambient temperatures between 71 and 98 F, varying speeds, uphill and down, I saw a range of coolant temperatures between 185 and 223 F. Average is about 200F.

Regards,

Mark
This is about what I saw too, driving Calgary to Vancouver in late May.

Peak temp reached 225F on the long climbs, with atf sump at 240F and oil temperature reaching around 280F. Coolant recovered first, the atf, then engine oil. Ambient temp was mid-70ís.
Iíve read that some have instrumented the exhaust manifold to measure Exhaust Gas Temp, and after watching my oil temp spike up I can understand why, but thatís for another thread.

-dave
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