Re: Synthetics???/

[rsco@lubrizol.com (Robert S. Cohen)]

"Bob D'Amato" <Bob.Damato%snetel.com> wrote
>Hate to bring up an old topic again...
>
>I just changed the oil in my car (90 20V) and replaced it with the Mobil
>1 synthetic oil.  5w30 (winter coming and all...)
>when I started the engine, cold, it read the usual 5+ bar. After it
>heated up a while, it read +-3bar at idle. Now I thought the whole damn
>point of synthetics is they dont lose their viscosity over the
>temperature range. Its no better than the old dino I used to use. am I
>missing something here??? Did I forget to carry the 2?? :)
>

Bob-

You aren't understanding what the weight numbers are telling you.

A 5 weight oil is relatively thin (at a given temperature).
A 10 weight oil is thicker than 5 weight at the same temperature.
A 30 weight is even more resistant to flow at that temperature.

A 5w30 specification on your motor oil means that when your engine is cold,
the oil will be as viscous (resistant to flow)  as a 5 weight oil at that
same temperature. This is important because oil needs to quickly reach
critical engine parts even as you are cranking the engine over. If it's
fairly cold, you'll want a 'thinner' oil that will quickly flow through
your engine.

The 30 in the 5w30 spec means that the oil is as viscous as a 30 weight oil
at operating temperatures.

Your pressure guage observation bears this out. When you started the
engine, it was cold, the oil was a little thick. The pressure was a little
lower later when the engine was hot and the oil thinned a little.

Had it been a straight 5 weight oil, your pressure would have quickly
dropped as the oil warmed and  decreased in viscosity.

*THIS IS THE WAY YOUR OIL IS SUPPOSED TO WORK

Synthetics tend to need fewer viscosity modifiers (high molecular weight
polymers, usually) than petroleum-based lubricants to attain these weight
specs. Viscosity modifiers break down with use. In that regard,
petroleum-based lubricants might 'lose' their viscosity more, but it's with
use, not with changes in temperature.

Disclaimer- I don't speak for Lubrizol.


_____________________________________________________________________________
Robert S. Cohen         rsco@lubrizol.com       Lubrizol Corp.,
NewMedia Inc.           ^^^ preferred ^^^       29400 Lakeland Blvd  MS 228,
Cleveland, OH                 -or-              Wickliffe OH, 44092
                        rsc2@po.cwru.edu        voice 216.943.1200 x 2012
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