Viscosity Index Warning Signs

Thanks Kumar.

A related query: with the addition of polymer into lubricant oil, any multigrade lubricant oil will behave as non-newtonian fluid. Why then, is VI used as one of the physical properties? Are these VI values only serves as indicators to oil's response to temperature variation?

John.

kumartr@enoc.com
Viscosity modifier (VMs)are added to alter the oil viscosty to increase at higher temperature and decrease at lower temperature (Pillow effect). If VM is not added oil viscosity will not either decrease or increase. Therefore Viscosity Index is not the creteria in judging oil condition in multigrade engine oil. There are many SAE papers to explain this mechanism.

Thank you for your comments, Kumar.

John.

quote:

However, I have yet to come across used oil analysis reports that considers a limit (caution/critical) to the degree of decrease in Viscosity Index over time.

I think most labs would have a condeming limit of when the oil "drops" off grade as in a 30wt drops to a 20wt then time to change out.
bruce CLS