How does a viscous fan work?

[diggerdog36]

As the title says, how does a viscous fan work? It doesnt spin all the time does it?

[mistericeman]

in simple terms imagine two sets of vanes ,independant of each other ,one attatched to the engine ,the other to the fan ,in a container surrounded by a liquid that gets thicker as it gets hotter ..........


when its cold the engine side turns ,the fan side stays still or rotates slowly ,as the liquid warms up it gets thicker and "locks" the two sections together to rotate the fan .........

[TEMPL4R]

When the engine is running slow or ticking over, the fluid drags the outer hub and fan to keep an air flow. When you speed up, the airflow through the rad is enough to keep the radiator cool and the fluid lets go of its grip as the revs get higher. ( fluid engineering)
If the rad and engine do get too hot, there is a coil on the front of the hub that senses it and physically locks the hub.

That's the easy to understand basics.

Chris

[bananahead]

EDIT: i was too slow :P now i have answers!

[bananahead]

actually i have one question if anyone knows.

Recently i had two of these, one was harder to turn than the other... Is one of them worn or something? The slacker one?

[TEMPL4R]

They do leak and get sticky up the back of the hub. The leak is where the hub nut goes in (obviously)

If you give a Viscous fan a tap, it should just move a bit. If it spins freely, it's had it.

Chris

[mistericeman]

a link to whats inside ..............


http://www.jag-lovers.org/xj-s/book/FanClutch.html

[diggerdog36]

Wow, cheers guys, wasnt expecting so many replies!! So if the fan spins permenantly and cant be stopped, is it broken??

Just, my Disco Td5 is over cooling when idling. The temp drops back down to cold if idled for 15 mins, or/and my thermostat is stuck open

[Widget]

The fan works approx 5-10% of the time only. The fludi does not thicken according to temperature - a bi-metallic strip responds to the temperature, opening and closing a valve which allows the viscous fluid to flow and engage the fan above normal operating temp.

You can also hear it engaged when the engine is first started. After about a minute it disengages.

[landowner]

Wow, cheers guys, wasnt expecting so many replies!! So if the fan spins permenantly and cant be stopped, is it broken??

Just, my Disco Td5 is over cooling when idling. The temp drops back down to cold if idled for 15 mins, or/and my thermostat is stuck open

I would shove a new thermostat in.

[TEMPL4R]

If it always draws air in it is seized. It will really blast air through and sound more like a jet engine.

When you stop the engine, it should move slowly with a bit of effort. If you can't feel a bit of drag, it isn't doing as it should.

Chris

[JulesV8]

So what does it mean when the fan is stuck fast when the engine is cold? does that mean its also had it?

On mine, its solid, even when cold...should I try when its hot?

Thanks

J

[TEMPL4R]

When it's hot it should lock up. The little coil on the face ( in the pictures ) does that.

It should move if you push the blades. If it doesn't, it's seized.

Chris

[JulesV8]

cheers for the info...mine is seized then. Ta

J

[Stu2985]

when is start up my fan goes fast for a minute then when it realises the engine is still cold it slows right down until its been idling over 5 minutes when it starts going fast again as the engine heats up

i assume then that its running correctly then ?

with the engine off should the blades spin easier when its hot or cold and in which direction (facing the engine) should I be pushing clockwise or anti clockwise ?

[TEMPL4R]

It can turn either way.

I have seen loads of people grab the fan while it's ticking over. They seem to think it a neat trick, until it is a seized one...:rolleyes:


Keep fingers away from the fan. Only check it while the engine is off.

Chris

[poseidon]

Hi - I'm a heretic, and I think the best approach to these viscous fans is to remove them entirely. The tdi engine never gets warm enough to need fan cooling in UK conditions and even with low gear off road work. It certainly isn't needed in winter and no fan = maybe 1 mpg better fuel consumption. Whack it off and bin it ;)....Keith

[Widget]

More lunatic than heretic I'd say.:eek: It's been covered before, but even if a Tdi needs a fan for only 1% of the time, it's still 1% that can boil it and cause HG failure.

[SCHREIBER]

Hi - I'm a heretic, and I think the best approach to these viscous fans is to remove them entirely. The tdi engine never gets warm enough to need fan cooling in UK conditions and even with low gear off road work. It certainly isn't needed in winter and no fan = maybe 1 mpg better fuel consumption. Whack it off and bin it ;)....Keith

I have a 200tdi 90, still fitted with viscus fan, and when I do low range off road 'work' it gets very hot, and overheated aswell??:confused: :confused: