Actually, it's correct the way I described it.
Oils are very linear with viscosity and temperature. Basically, the warmer you
get them, the more they pour like water. The colder you get them, the more
they pour like molasses. The SAE designation of viscosity (weight number)
describes just how far up or down that process of thickening and thinning they
are.
A 30 weight oil (straight weight) would move like a lump of tar when it's cold,
like on a frosty morning. Warm it up to something like 80 degrees F (a summer
day) and it pours like thick water. This makes a straight 30 weight oil good
for summer, but bad for winter.
A 10 weight oil would move like thick water on a frosty morning, but be so thin
on a hot summer day it couldn't build up pressure. So good for winter, but bad
for summer.
This meant you had to keep track of your oil types, and change them with the
seasons. Quite the pain for most car owners, though it is still done for many
types of equipment (straight weight oils are stronger then multi-weight oils).
Along comes multi-weight oil. This is the best of both worlds. It flows like
a thin oil when its cold, and thickens up when it's heated. Yippee! No more
changing oil just because of the seasons.
Take 10w-30 for example. On a cold morning, it will flow like a 10 weight does
in the same cold. Warm it up, and it now will flow like a 30 weight does when
it's warmed up to the same temperature. The net effect is that a multi weight
oil tends to pour like thick water no matter what the temperature. Hence the
multi designation.
http://www.micapeak.com/info/oiled.html
This web page has quite a bit of information on motor oils in it btw.
>>> "Ptegler" <ptegler@gouldfo.com> 05/31 9:16 AM >>>
Still a bit scrambled/confusing there Nolan.
...staying with your angle of description....
For a 15-40 The 40 is the 'cold pour' viscosity.
The 15 is what it would be turn into after warming up.
so...
>> The 15 (cold pour) side of a 15-40 weight oil can make it a bit thick to
>pump on a cold morning >>
- Should read the other way around. It would be the 40 that would make it
'stiff' on a cold morning.
You got the rest of the definition/comments 'fairly' right... just reversed
the # terminology a bit
made the rest of it seem backwards.
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