Mys Terry wrote:
On Tue, 06 Jun 2006 15:07:15 GMT, Gene Kearns
wrote:

On 6 Jun 2006 07:21:41 -0700, "basskisser" wrote:



One thing about multi viscosity numbers is that in a 10W-30 for
instance, the 10 doesn't correspond to any temperature! It only means
that the oil will flow when cold like a straight 10W will. The 30 on
the other hand, means that the oil will act like a straight 30W at a
given temperature, which is 212F.

The above is the oral tradition carried on, but is totally incorrect.

For starters see:
http://www.texacoxpresslube.com/carc...viscosity.html


From the link you gave:

The reason we have both single grade and multigrade oils is largely
historical. The earliest engine oils were all non-W single grades, but
as the requirement for oils to work well under both low and high
temperatures evolved, W grades and multigrades emerged. In terms of
viscosity, the biggest difference between a multigrade and a single
grade is that the multigrade must not become too viscous at low
temperatures, while still meeting the requirements of its high
temperature grade - in other words, multigrades exhibit less viscosity
change with temperature than most single grades.

Thus, a typical 5W-30 motor oil has the same approximate kinematic
viscosity as a SAE 30 grade oil at 100 ° C, but it's viscosity at very
low temperatures, while thicker than when hot, is much less than the
30 grade. This is achieved by formulating multigrades with a higher
Viscosity Index than typical for single grades. So, while a 5W-30 oil
will allow a modern car to start at temperatures as low as -30 ° C,
the typical SAE 30 oil would be too thick to either crank or pump at
that temperature.


Sounds like the oral tradition is also the facts!

That's why I'm confused! Gene's sharp on this subject, I'm sure he'll
clarify.