Thread: Viscous fan Temp

Viscous fan - right ?
The belt driven fan - right ?

It always spins when the engine is running, just with slip at times.
Even when it's not fully engaged (slipping), I doubt you could stop it spinning with a straw !!

I was going to post a question about this myself, seeing you have i might ask too.

Mine came on this morning, you know that sound it makes when it gets hot a sort of growling sound, well it has never cut in when it's been cold only when hot, any ideas.

Baz.

I think it is normal for them to work from dead cold start, then cut out (go quiet). Then only shift air (loud operation) when it is hot enough to warrant it.

Originally Posted by BigJon

I think it is normal for them to work from dead cold start, then cut out (go quiet). Then only shift air (loud operation) when it is hot enough to warrant it.

how hot is hot though???

Originally Posted by BigJon

I think it is normal for them to work from dead cold start, then cut out (go quiet). Then only shift air (loud operation) when it is hot enough to warrant it.

Maybe i've just never noticed it before, i know on really hot days when out 4wdriving and only going slow it does come on alot, i put that down to less airflow at low speeds.

Baz.

Originally Posted by TREX

how hot is hot though???

When it is hot enough to start working . Dunno about a spec, will see what I can dig up.

Originally Posted by BigJon

I think it is normal for them to work from dead cold start, then cut out (go quiet). Then only shift air (loud operation) when it is hot enough to warrant it.

Yes. After sitting the silicone fluid pools so that on start-up, the viscous coupling is engaged. After it's been spinning for a short while, the fluid distributes and the clutch slips.

Originally Posted by RAVE

Viscous fan

There are two main components of the viscous fan drive : An input (drive) member consisting of a threaded shaft passing through a bearing into the clutch plate and secured to the water pump. An output (driven) member comprises the main body to which the fan attaches, with the temperature sensing mechanism (bi-metal coil) and pump plates. The fan drive only has to be engaged periodically, between 5% and 10% of the time during normal driving conditions, because usually the vehicle is cooled by ram air.

A bi-metal coil senses air temperature behind the radiator. When a pre-determined temperature is reached, the coil opens a valve which allows fluid to enter the drive area. Centrifugal force circulates the fluid to the annular drive area. There are two sets of annular grooves, one in the drive clutch and the other in the drive body, a specific clearance being provided between the two sets of grooves. When this clearance is filled with viscous fluid a shearing action, caused by the speed differential between the two drive components, transmits torque to the fan. The fluid is thrown to the outside of the unit by centrifugal force from where it is then re-circulated to the reservoir via the pump plate adjacent to the drive member. If the engine speed is increased, the amount of slip will also increase to limit the maximum fan speed.

When the air temperature from the radiator drops sufficiently, the bi-metal coil closes the valve and prevents fluid entering the drive area, see figure 26M7026. The fluid that is in the drive area will gradually pump out into the reservoir and the fan will return to an idle condition.

Hi Baz
Next time yours is on note if the aircon is off.The D2 temp gauge seems to sit in the middle regardless of it getting hot.The booster is controled by the ECU.
Im thinking its your electric booster fan cutting in,much louder than the engine driven fan.
Try turning the aircon on at about the same speed/revs you do when off-roading with the window open,it will confirm if its the booster.
Once a overheat is registered that fan will run all the time until cleared by testbook.Even if the gauge hasnt looked like getting hot.
Start checking for bulging radiator hoses when hot,smelling slight sniffs of coolant after a hot run.Signs of a headgasket starting to leak.If you get it early you should getaway with the gasket only(and dowels if you still have plastic ones).
Hopefully Im wrong,but thats how mine started.
Andrew