BFG All terrains and fuel economy - now heading off topic

G

Guest

Guest
Pity I like the word "thixotropic", "dilant" or "rheopectic" won't stick in
my mind as well.
Thinking about it I don't know where I got the term connected to VC's, it's
been in my mind for quite a while, probably something I was told when I had
the freelander. Google come up with lots of thixotropic silicone references
but looking at them the seem to be related to processes for making moulds
and such like where the description Chris gives makes sense.
Seems a common misconception - Hyundai web site has a data sheet google
found which claims a thixotropic VC.
http://www.hyundainews.com/assets/Media_Kits/2005_Models/Santa_Fe/asset_uplo
ad_file690_1089.doc
Would be interested in knowing if it the VC fluid has a dilant or rheopectic
characteristic, I am guessing dilant otherwise the slip would be only slowly
decreasing and considerable heat would be generated, but that I have read
this evening that some Limited Slip Differentials use a viscous coupling
which would have to allow considerable slip to work.
Always learn something on ELCO.
Malcolm
Stafford (UK)
FJ45 '75 & FJ45 '76
-----Original Message-----
From: [Email address removed] [mailto:[Email address removed]] On
Behalf Of Christopher Bell
Sent: 07 May 2009 18:37
To: [Email address removed]
Subject: RE: [ELCO] BFG All terrains and fuel economy
Andrew
| To add my 2 cents - yes, almost right, Chris. The fluid behaviour you
| describe is dilatant. This is different from rheopectic in that a
| dilatant solution goes from being viscous to almost solid pretty much
| instantly when subjected to shearing forces. A rheopectic solution
under
| shear increases its viscosity over time (i.e. it gradually gets more
and
| more viscous as it's subjected to more and more shear).
|
| I never thought my degree in chemical engineering would come in
handy!!
| For an easy example of how a dilatant fluid works, make a corn flour
| solution at home - add corn flour to a cup of water until you have a
| "runny" paste (slightly runnier than yoghurt) by mixing in SLOWLY.
Then
| try stirring fast and see what happens;-)
| Not sure that a corn flour mixture would make a good substitute for
the
| silicone in your V/Coupling though - might start to smell like toast
| after a while!
Well I learned about it (thixotropy that is) while reading Civil
Engineering, so it's a small world isn't it? I have a daughter reading
Chemistry at Bristol at the moment, but everything she says goes way
over my head.
I got cold feet and decided to re-measure the tyres, and have now
decided that the difference in diameter is more like 5mm - it's actually
quite hard to measure without a Tee square or something similar - and I
simply refuse to believe that a small difference like that will upset
anything. So I'm officially sticking my head in the sand on the subject
of cooking VCs!
The truck is due for an oil change this month, it tends to do better MPG
in the summer anyway (higher ambient temp? higher cetane rating in
summer diesel? Who knows!), and I think I'll put in a new air filter too
just in case. Hopefully that will help a bit.
CB
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