<VV> <WW> Oil Viscosity

[Jim Becker]

I don't know where the term oil "weight" come from either, but assume it is 
rooted all the way back to the earliest crude oil refining process.  It was 
essentially simple distillation.  When crude is heated, different components 
boil off at different temperatures.  The shortest molecules, starting with 
methane, come off first.  Farther down the mix are longer (and heavier) 
molecules that make up other petroleum products.  Lubricating oils are 
fairly well down toward the bottom, but not quite down with asphalt at the 
bottom.  I assume that light/heavy lubricating oil is a finer split within 
that separation.  Current oil technology has developed to the point that I'm 
not sure how much of this is even relevant.  A can of modern petroleum based 
oil is only about half oil, the rest is additives.

Anyone that wants to see an example of where oil "weight" is still used with 
classifications of "light", "medium", etc. to indicate viscosity can take a 
look here:
https://www.mobil.com/en/lubricants/for-businesses/industrial/lubricants/products/products/mobil-vactra-oil-heavy-medium
Until SAE came up with the 10, 20, 30, etc. viscosity numbers, this is how 
motor oil was classified as well.

Jim Becker

-----Original Message----- 
From: Jim Simpson via VirtualVairs
Sent: Sunday, August 09, 2020 5:24 PM
To: jf at shibboleth.com ; Virtual Vairs
Cc: Jim Simpson
Subject: Re:   Oil Viscosity

0W-30 oil does not have "zero" viscosity, rather the 0W refers to how the
oil acts at low temperatures.  (The "W" means winter.)

Here's a good reference:
https://www.bobistheoilguy.com/putting-the-simple-back-into-viscosity/

Scroll down to the tables and you will see that "0W" oil has a viscosity of
3250 centipoise at -30 deg. C.

The 0 (zero) refers to oil "weight", an old term that has essentially lost
its meaning over time but is still used in the oil industry to describe
lubricants.  I've never found a good source that describes where the term
came from, but the SAE has come up with definitions for what the various
"weight" oils are in terms of viscosity at various temperatures.

Jim Simpson
Group Corvair
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