Q on viscosity index

[koreancar]

Not sure if this is the right place to post this...

Is viscosity index a good indicator of an oil's quality ?

Let's say I'm looking at the spec's for a 5w30 grade oil on Redline, Mobil 1, and Royal Purple.

Does it mean the oil with the higher V.I is a better quality oil ?

 

[Curious Kid]

Well, good numbers can be misleading. I will say from what I have read, synths or base oils of higher group number have a higher natural VI. However, and this is where some misleading may be presented, is that some VI improvers may be added, inflating this value. In use, these VII will shear to some degree. Just how much is anyone's guess, though a used oil analysis will show - reference other's UAO's in the BITOG's library. Oil type, engine, service type, etc. all go into having an effect on the oil's durability.

Just my "2 cents".

 

[XS650]

Not by itself. A high viscosity index can be obtaind by the use of cheap viscosity index improvers. Or it can be obtained by the use of hgher quality VI improvers or inhererently in the synthetic oil manufacturing process.

The cheap VI improvers will shear out early and leave you with a low VI oil. An oil with good VI improvers or asynthetic will hold it's VI a lot longer.

 

[TallPaul]

Redline 5w30 is supposed to have zero VI improvers.