"Gene Kearns" wrote in message
...

On Tue, 06 Jun 2006 19:07:23 GMT, Mys Terry penned the following well
considered thoughts to the readers of rec.boats:

On Tue, 06 Jun 2006 18:43:28 GMT, Gene Kearns
wrote:

On Tue, 06 Jun 2006 15:30:26 GMT, Mys Terry
wrote:


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!


Really? Show me where it says 0W-40 oil acts like 0 weight (no
viscosity?) oil when cold and 40 weight oil when hot......

Answer: 10W-30 does NOT become 10 weight oil when cold and 30 weight
oil when hot......

Turn your binoculars around the other way, Gene. 10W-30 performs like
10 weight when it is cold, and as it gets hotter, it doesn't thin out
as much as straight 10 would. When it's at 100C it is about the same
viscosity that straight 30 would be at that temp.


"multigrades exhibit less viscosity change with temperature than most
single grades."


Ok, I can see that you wish to believe that "10W-30 performs like 10
weight when it is cold, and as it gets hotter, it doesn't thin out as
much as straight 10 would. When it's at 100C it is about the same
viscosity that straight 30 would be at that temp."

That certainly is your right... but if you spend as much time reading
on the subject as I have.... you'll see things differently.

10W-30 behaves exactly like extra virgin olive oil. Mah daddy done said so.