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Viscous Fan Workings


Guest David William Hunt

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Guest David William Hunt

I remain confused as to how the viscous fan on the 2lt is meant to work. Im told that at a certain rpm the assembly slips and somehow this saves energy! Is this the function and purpose of this device?

I notice that the fan blades on my car can be pushed around quite readily( without the belt moving) but on a friends car the fan blades hardly move when pushed by hand--which is the correct condition?

Also Im told that when it fails the device locks up and fan blades can shatter. How can this be  as a locked solid device would only be replicating the situation on a fan without a viscous slip.

Finally  the unit on my car has been emitting a high pitched whistle which goes away when I squirt some WD40 into the ring ( is it on the way out?) Looking forward to any feedback from viscous fan experts!

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I would suggest that the correct condition is somewhere between you and your friends car, difficult to guess without trying it, maybe you should try a third car. The fan is meant to slip as the revs get higher, as you would really only need the cooling effect at tickover in traffic. Don't forget that the air resistance to the fan blades will increase at the square of the blade speed, so it will slip more at high revs. The blades are not designed to run at high speed, so could shear off if run too fast. I'm not sure whether the whole fan comes off, or the blades just shear if the bearing seizes, but I gather the end result is usually a damaged radiator! The bearings are going in yours!

 

Ray

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  • 2 weeks later...

The engine is powering the fan to draw the air over the radiator.  When it's slipping no energy is transfered to the fan so that energy is available at the gearbox instead i.e. you have better efficiency because you are not powering unnecessary auxilliaries.

 

This is achieved in modern cars with an electric fan which only runs when needed and quite a common modification to do on a TR7.

 

It sounds like your's is free wheeling the whole time so you are probably getting little or no benifit from the fan and you may get overheating problems in hot weather and slow traffic.  Its unlikely to shatter in this case as its not doing any work!

 

My viscous coupling has done the opposite and seized completely and been so for probably 5000 miles.  I'd not heard about the problem about the blades coming off so I need to do something about it.  Now moved a few places up my list of to do jobs!

 

Ian

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David

      I had the same thing with the fan on my old TR7 and did as you do squirt it with WD40 and that stop it well untill the day the fan came off and took a lump out off the radiator with it. If you look in the part book you see that there a ring thing that keep the fan on this have broken up so the fan was just sliping if you see. As to the fan shattering my was happy with braking up the radiator with out doing so. I would give it a pull and if it look lose get it fix our take it off and put a electrical one on.

             David

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Guest David William Hunt

Thanks for the info. and advice---------looks like another winter project. I was tempted to leave it till it breaks but the consequences of doing this sound like a risk not worth taking

 

David

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I would not leave it if it on the way out my whent as I was leaveing the Lakes and end up comeing home with the RAC but it did make one RAC man happy as he got a day over time out off it, and I had all the spare parts in the shed to fix it, think I had it up and runing befoe he got back home.

                 Peter

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  • 1 year later...

As PeterH says, don't leave it. My 'work in progress' started to make a noise about 2 weeks before the inevitable happened.

 

I had my suspicions as my car was seldom used before I bought it. Although the fan checked out under a visual inspection, the engine felt tight under acceleration & the fan was causing resistance as it was engaged throughout the rev range. After reading the posted threads I ordered a new viscous coupling which was extremely expensive and waited for it to arrive.

 

In the mean time the noise got worse. It sounded like it was coming from the transmission tunnel. Then, one afternoon, the noise just vanished. While I was glad to be able to hear the radio again rather than use it to muffle the screeching noise, I was nervous as to why the engine felt nice and free revving. Curiosity got me to pull over and check the fan. Luckily, it was still in one piece. Unfortunately, it was embedded in my radiator.

 

From first noticing the problem to ending up with an expensive failure was less than a fortnight and under 200 miles.

Edited by sunnymac
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