point of viscous?

[96terrano]

hi guys, im just wanting to learn here:)

i sort of know how a viscous fan works, but why is a coupling needed? why is the fan not just bolted to the engine? is the coupling their so the fan is able to spin slower? i don't see the point of it, can someone explain;)

[solarman216]

viscous fans work something like a torque converter on an auto gear box, there is a bi metal coil spring on the front of the unit which is sampling the heat from the rad all the time if it gets hot enough it opens a valve that triggers the fan to run at full water pump speed, as the temperature drops the valve closes and the fan goes into normal idling mode, the reason it starts at full speed is cos the viscous fluid has sunk to the lower half of the coupling and so drives the fan positive until it disperses the fluid to the outside, Rick

[96terrano]

viscous fans work something like a torque converter on an auto gear box, there is a bi metal coil spring on the front of the unit which is sampling the heat from the rad all the time if it gets hot enough it opens a valve that triggers the fan to run at full water pump speed, as the temperature drops the valve closes and the fan goes into normal idling mode, the reason it starts at full speed is cos the viscous fluid has sunk to the lower half of the coupling and so drives the fan positive until it disperses the fluid to the outside, Rick

Thank you rick, that's helped greatly:bow:thumbs, I thought my viscous was broken because it roared when on motorways but it's probably because the engine runs cold their so the fan idles

[rustic]

Thank you rick, that's helped greatly:bow:thumbs, I thought my viscous was broken because it roared when on motorways but it's probably because the engine runs cold their so the fan idles

At the start of my journey, from cold I can hear the fan, after a few hundred yards I can hear the fan start to slow down.
It has done this for 17 years without a hick up, in fact I can usually get to the end of village at the same point each time when I hear the change.

[solarman216]

At the start of my journey, from cold I can hear the fan, after a few hundred yards I can hear the fan start to slow down.
It has done this for 17 years without a hick up, in fact I can usually get to the end of village at the same point each time when I hear the change.

that is correct operation, but just a word of caution, I did my engine when towing on a hot day slow up hill, my fan behaved just as yours does BUT when the engine got really hot it DID NOT CUT IN, by the time I stopped it was too late, bi metal coil on the front was not doing its job, so binned the viscous and fitted electric, as I could find no reliable way to test the viscous for opperation when hot, Rick

[dollywobbler]

Is the fan roaring any other time Ryan and how cold is it running? Mine sits at one third on the gauge and the fan never roars apart from at start up.

The actual reason for fitting a viscous unit is that it should save energy by not putting as much drag on the engine. It should also stop if it hits deep water whereas a solid fan will try to keep going, either damaging the fan or stalling your engine.

[Lazy-Ferret]

I love the roar from the fan when you first start it, it is one of the things that makes it sound like a real "truck" meant for the job.

The only time I have heard ours, other than start up, is on the motorway on a hot day, after completing a bit of a climb, and I must admit I was surprised just how loud it was, and the first time it did it, I did wonder what the noise was.

I have had viscus fans on several of my early Volvo's, and a few other cars, and never had much of a problem with them, although ironically I have had several electrical thermostats or their relays pack up resulting in the electric fans not coming on.

[96terrano]

At the start of my journey, from cold I can hear the fan, after a few hundred yards I can hear the fan start to slow down.
It has done this for 17 years without a hick up, in fact I can usually get to the end of village at the same point each time when I hear the change.

thats the same as mine lol, it usually changes when climing the hill out of my town:D