"Vic Dura" wrote in message
...
On Mon, 20 Jun 2005 15:25:08 -0500, in alt.home.repair 5w-20
motor oil Duane Bozarth wrote:

Vic Dura wrote:

...
I always thought that the second number e.g. the 20 in 5w-20 indicated
the high temperature lubricating ability of the oil. So for 5w-20 the
oil flows/lubricates like 5w oil when cold and like 20w oil when hot.
Then going from 10w-40 to 5w-20 would mean that when hot the engine
oil flows/lubricates like 20w oil instead of 40w oil.

Is that correct or am I miss-understanding all of this?

Except that it's only the (approximate) viscosity being indicated, not
the lubrication properties. That's specified by the SAE letter
designation (SE, SF, etc.).

Ok, thanks for the comments. I think I have a better understanding of
it now.

The viscosity measurements are made at 0C (32F) and 100C (212F).

So for 5W20, at 0C the viscosity is the same as straight weight 5 at that
temperature.

At 100C the viscosity is that same as straight weight 20 at 100C.

Still while warming up the 5W20 still thins. It has higher viscosity when
cold than when hot.

I suggest a synthetic because it does not have Viscosity Improvers.

There are some good sites about oil around the web:

http://www.chris-longhurst.com/carbi...oil_bible.html