PLEASE READ - RE:confused about synthetic gear oil

[R Mangas]

   No, the vis rating on the oil is at a pair of specified temperatures.  As
I recall, the second (hot) number is at 100C, while the test temp for the
lower temp number varies somewhat.  The deal with synthetic lubricants is
that they can achieve viscosity span x with less added viscosity improvers,
which are more sensitive to breakdown and ineffective once broken down.
This is why conventional oils with a wide viscosity span are to be avoided
but buying 5w50 synthetic isn't as crazy as it sounds.

  $0.02,
Robert




>From: "Livolsi, Stephane" <Stephane.Livolsi at investorsgroup.com>
>To: "Robert Deutsch" <rdeutsch at sk.sympatico.ca>
>CC: "Audi Quattro List" <quattro at audifans.com>
>Subject: RE: PLEASE READ - RE:confused about synthetic gear oil
>Date: Tue, 25 Feb 2003 11:34:59 -0600
>
>I hear you and agree except for one thing..
>
>I did a bit of research about oils (synth and regular) before deciding on
>the amsoil 80W90 GL4 synthetic.
>I am sure that somewhere, I read that synthetics maintain their viscosity
>range over a broader range of temps.  Isn't that correct?
>
>So a non-synth 80W90 will have that range of viscosity over temps of say
>-10
>to +50 C (pulling #'s out of a hat)
>a synth 80W90 will have that range of viscosity over temps of say -30 to
>+70
>C  (also pulling #'s out of a hat)
>
>I could be wrong, I'm willing to learn...
>
>Stephane
>
> > ----------
> >
> > When it comes to how "thick" an oil is, the viscosity is the measure of
> > the "thickness". The use of two numbers in the viscosity ratings of oils
> > such as 15w40 shows the range of the oil's viscosity. So a conventional
> > multi-grade gear oil with a viscosity rating of 75w90 is the same
> > "thickness" as a 75w90 synthetic gear oil, only the synthetic oil will
> > break down slower. The higher the viscosity rating numbers (especially
> > the second one of the two), the "thicker" the oil is. Now, one thing
> > that people should also keep in mind is that different oil companies may
> > use different processes and include different detergents and additives
> > in the oils which may make two oils of the same viscosity seem
> > different. Also new oil will perform differently from used oil so there
> > may be a change in apparent "thickness" after a fresh oil change.
> >
>


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