[BiturboS4] engine oils

[California Fields]

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Lance, you  bring up a good point - that dino oils need viscosity improvers
(long-chain carbons) in order to enhance their lubrication properties at high
temps...but that these viscosity enhancers tend to break down at high temps
over time thus resulting in insufficient protection over time (a 10W40 dino
oil may truly become a 10W30 over a short period of time).  Synthetics, on the
other hand, need less viscosity improvers since they are inherently better at
meeting the spread of viscosities...and, therefore, they won't breakdown as
easily.

Another good point (which I can't find definitive evidence of) is that the
viscositiy improvers don't actually help lubricate the engine...they just
improve the viscosity.  This is worrisome but, again, I can't find any info
proving this.

Needless to say, it looks like synthetics are the best way to go.  I'm just
trying to find out which one of the synthetics is better than the others :)

One final thing, though...I've heard many people say on various newsgroups
that dino oil is better for a brand new engine (i.e. don't use synthetics
until after 10k miles or something like that). I can't understand why this
would be true.  Anyone have an idea?

I'm still compiling additional info on oils.  More to come....

-Carter, 2001 S4 (stock), San Francisco.
>Carter,
>
>One thing you haven't touched on is the issue of Viscosity Index
>(the ratio of viscosity decrease to temperature increase) and VI
>"improvers". My understanding is that synthetic based motor oil has
>a higher VI than any crude base (don't know anything about the base
>of "psuedo synth"). In order to bring the VI up to the levels needed
>for 10W30 or 10W40 the motor oil manufacturers add special long
>chain hydrocarbon molecules to the mix. These compounds coil up
>into short "chunks" when cold and unwind into long "strings" when
>hot. The longer the molecules become the more they increase the
>viscosity of the base oil. There are two issues with this. One is
>that over time the long chains get sheared into shorter chains
>resulting in a loss of VI. The other is that there is AFaIK some
>suspicion that while VI improvers do indeed make the oil more
>viscous at elevated temps they may not actually cause the base oil
>to lubricate (prevent metal to metal contact) any better at high
>temps than the same oil would do without the VI improver. In other
>words from a pure lubrication perspective the petro based 10W40 may
>be no better at protecting cylinders and bearings than a straight 10
>weight oil at high temps. The VI improvers do prevent the loss of
>oil pressure at high temps that would otherwise occur if a straight
>10 weight petro based oil was used so there is definitely some
>benefit but since synthetics have an inherently higher VI and little
>or no VI improver is needed to produce a 10W30 or 5W30 these
>concerns are minizmized.
>
>I've also been told many times that synthetic based oil carbonizes
>at a much higher temp than dino juice. I don't really know if this
>is true or just an OWT but based on what I have heard I believe it
>to be true. I wonder where the psuedo synthetics are in this regard?
>
>-lance
>

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