How does the Viscous Fan Work?

[atomic]

Hello, being a new memeber and the proud owner of a totally original 109" County Station Wagon I am appealing to you experts on the the topic of viscous fans!
I am not sure if mine is eworking "properly" is there a way of checking the function easily? I ma guessing thaty when the temperature is high enough the fan should not be rotateable when the engine is off?

[Huzey]

Hi Atomic and welcome to the forum
Now then, lets see if I can remember my college stuff about viscous couplings.
I think we have got the torque limiting type of coupling on our motors, so when the fan, being driven by the drive belt reaches a certain speed, it cannot go any faster because of the viscous drag of the fluid, (silicone) and it's resistance to shear, so this is more efficient than a direct driven fan as it doesn't use so much power.
The other type of coupling is an air sensing fan drive that, as well as torque limiting, also varies the fan speed to suit the temperature. When the coolant is below a certain temperature, the sensor (bi-metalic spring) doesn't allow any fluid to the drive plate, so it doesn't turn the fan, saving power and getting the engine up to operating temperature faster. When it reaches the required temperature, the fluid is allowed into the chamber in the aluminium hub, connecting drive to draw the air through the radiator.
I think the main fault is they sieze up so you have got a direct driven fan, that defeats the object of the viscous coupling, or they loose fluid or the bi-metalic spring fails, and end up with no drive at all.
Hope this makes sense and is of some help to you.
Regards Huzey

[dennis]

I ditched mine for an electric fan (Well its still in the shed with the cowling)
With time they 'stiffen up'. You should be able to stop the fan quite easily when its running (Very dangerous, silly, and do it at your own risk) but its how my semi-tame mechanic tested it
Anyway, i chaged mine to electric so the engine heats quicker (handy 'cos i run Duel fuel and the LPG don't like frost!) and if you go thru deepish water you can make sure its off so it doesn't spray the dizzy and coil with water !!
I used a fan unit from a volvo V70, as with a slight trim the whole assemby drops into the cowling space a treat.

.. I also drive a volvo. As my V8, Lulu, and Vicky, the S40, are cousins by marriage they get on very well. Pick on Vicky and 1.8 tons of Unrestricted military Lulu will be having a word

[atomic]

May be its just the Volvo drivers down here who drive the country roads like they own them, until they see Dennis [the Menace] comming towards them. I think I am going to stop the kids giving the vehicles names
I will look out for a V70 fan.

[Bumpkin]

I drive an 850 T in my job. Great car!
Tel

[dennis]

However I must admit that if I see a Volvo estate with two big dogs in the back and a bloke in a hat driving... I go the other way