Viscosity Index numbers?

Messages
358
Location
Kewaunee WI
What do the Viscosity Index numbers mean? I have been comparing M1 5W-30 to RP 5W-30 and I see that RP is 157 and M1 is 169. What does this mean?
 
Messages
834
Location
CT, YL of USSA aka Oceania
There are too many variables that attribute to the VI spec: adpack chemistry, base oils, % of each to name a few. Don't place too much on this spec. There are dino and syn oils that have low VI's, turned good UOA's, and users have had engines lasted a couple hundred thousand miles without a problem using a low VI oil.
 
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