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 Post subject: Educate Me - Viscous Fan
PostPosted: Thu Nov 16, 2017 2:56 pm 
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Noticed the other day that my fan was on, even though I had only done a short trip. Seems to be on all the time? Engine off and cold, I can turn the fan and feel slight resistance from the viscous fluid. Weather has turned cold here of late, so is the fluid more viscous/likely to engage. I don’t really understand the reasoning behind the viscous fan. Up until now, I understood, coolant got too hot, switch brought fan into play. Anybody care to explain?


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 Post subject: Re: Educate Me - Viscous Fan
PostPosted: Thu Nov 16, 2017 3:03 pm 
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For gas KJ's................

Only way to get the mechanical fan is with HD cooling(tow package and/or offroad package).The electric fan is the main cooling fan and will turn on at 219 degrees and the mechanical fan is the AUX cooling fan.The OE clutch is spec'd to "lock" at 230 degrees.The 1st few mins after start up the mechanical fan should be engaged till the fluid inside of it evenly distributes itself and then it will almost totally disengage till reaching 230 degrees(OE fan clutch).


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 Post subject: Re: Educate Me - Viscous Fan
PostPosted: Thu Nov 16, 2017 3:22 pm 
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Location: Utah
Old-Bugga wrote:
Noticed the other day that my fan was on, even though I had only done a short trip. Seems to be on all the time? Engine off and cold, I can turn the fan and feel slight resistance from the viscous fluid. Weather has turned cold here of late, so is the fluid more viscous/likely to engage. I don’t really understand the reasoning behind the viscous fan. Up until now, I understood, coolant got too hot, switch brought fan into play. Anybody care to explain?


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The thing isnt perfectly frictionless, so its always going to be spinning if the engine is spinning. Before the clutch is engaged the fan is spinning at some speed less than the pulley in hopes that it reduces the load on the motor. When the viscous clutch engages then it brings the fan's RPMs more in line with the pulley RPM and starts to move more air but also draws more power.

The only way you will have a fan that doesnt always spin is if its electric and its not physically connected to the engine.

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