Viscous Fan Coupling - How To Test ??

Submitted: Monday, Jan 01, 2007 at 21:54
ThreadID: 40778 Views:33985 Replies:9 FollowUps:2
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Hi guys & Happy New Year to you all,
I've been nursing the cooling system along on the 4.5 auto 80 yota, but l want to iron out the symptoms so l repair only as needed.

On v.high temp days, crawling along in traffic, the temp starts to climb towards the red. Other days and/or not crawling along, it remains rock solid at about half gauge level.
I know the header tank has a slight leak along the crimped joint. The apparently it's not repairable as the rad is old - New Rad = $$$$ great start to N.Yr.
But is the viscous fan drive faulty too??

A mate reckons that when the parts are new, you can grab the input and ouput shafts of the viscous unit and as they are turned against each other (a lot!) the 'coupling' between them stiffens up. Thus on an old part, if it doesn't stiffen or is solid/seized - it's no good.

It was also said that you should be able to stop the fan (at idle) with a folded bit of cardboard but as revs are increased, the fan will 'couple' and drive 100%. However a US website says if you can stop it at idle, its buggered anyhow. Confusing, contradictory advice!

As mine is in the car, l cant try the 1st idea. However the fan is driving and wont stop with a bit of cardboard - it's not seized either. What does that mean?

Another sympton mentioned to me is that a lazy viscous coupling will affect the a/c ability to cool the car. My old R12 system is now filled with R143a (plus new drier) and doesn't cool as well as it used to either, thus swaying me toward thinking that the viscous coupling may be lazy.

Any other ideas on how to test this would be appreciated.
Cheers
BoB
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