Fan clutches are somewhat of a viscous coupling. More blades load the coupling more, slowing the speed of the fan when the clutch is not fully engaged.
They are absolutely a viscous coupling. Yes, more blades, or blades with a higher pitch load the coupling more, slowing fan speed. Whether this moves less air is debatable; and I have no idea how this affects noise.
What I don't understand is why his truck requires a "Severe Duty" clutch. I wonder if the description on the O'Reillys web pages is wrong. I get that "HD Towing Package" probably gets a bigger fan, bigger radiator, maybe. Maybe a different pulley ratio on the water pump. Who knows? A HD or Severe Duty clutch isn't out-of-the-question. But a more ordinary vehicle with AC but no "HD Towing" needing a Severe Duty clutch to drive a what is probably a base-model fan? I don't get it. A "Severe Duty" clutch has less slippage than a "Heavy Duty" clutch, which has less slippage than the ordinary thermal clutches. (Non-Thermal clutches are junk and shouldn't be considered.)
My point is, he's maybe got a 5-blade fan just like the one on my K1500, he's got severe fan noise when cold, and
I don't. His clutch must be locked-up (
faulty) when cold, because they're NOT SUPPOSED TO DO THAT. MAYBE it releases as it warms up, maybe is locked 24/7/365 and he doesn't notice it after awhile. I dunno. When the fan clutch locked-up on my Nova, it was so friggin' loud at highway speed that you couldn't hear yourself think.
My 5 bladed sounded like an airplane all the time. My 11 blade was virtually silent by comparison
Some of that may be due to blade design. The molded-plastic fan blades seem to be more sophisticated in terms of shape than the stamped-metal ones.
and my Duramax fan would only make noise for the first 1/8 mile or so
I'm surprised it took that long to quiet down.
When the Duramax fan would engage my a/c temps at the vents would drop below freezing and actually cycle the compressor off. Even at idle the Duramax fan pulled as much air as electric setups. I will also say that my water pump and at the time fan are 33% underdriven compared to stock with the March pulley set.
Nice!