VI and VII

[wemay]

I often read and understand that the higher the VI, the better or higher quality the oil is. I also read that the VI, though, is often influenced by viscosity index improvers (VII). How can one tell if its the base stocks contributing to this number or VII boosting it?

 

[CATERHAM]

The viscosity index (V.I.) of a motor oil is totally influenced by the polymer VIIs it contains and virtually all oils use VIIs to achieve the final KV100 and HTHSV of the finished oil.
Even the few specialty oils that are reputed to contain no VIIs still use polymer dispersants that increase the VI of the finished oil.

 

[MolaKule]

Originally Posted By: wemay
How can one tell if its the base stocks contributing to this number or VII boosting it?


You can't.

Even when using real and fully synthetic base stocks with high Viscosity Indices, formulators may have to tweak the PCMO formulations with a very small percentage of Viscosity Index Improvers to meet spec.

The exception is jet engine lubricants where expensive polyol esters, with inherently high VI's, are used.

 

[wemay]

Thank you guys.

 

[JAG]

A Harman in another thread said how to calculate the amount of temporary shear, which comes from the type and amount of polymeric VIIs, if present.