Tat, it's simply good to know.
And yes I'd like to know if any oil can match or better RLI.
What's RL's 100C visc. If it's 9.24 ..then it's easier to get a broader VI. If it's 8.2 ..you're slamming down toward the floor (the other end of the limits)
Bruce's 0w-10 only has a VI of about 150. It's got nowhere to go but down.
Beyond all that, I don't think it's a point of merit ..beyond a certain point on the lower visc fluids. How much limbo is productive.
Gary, Red Line's 0W-20 vis 100C is 8.2.
Part the reason for inquiring is that 0W-30 and 0W-40 grades have VI's in the 180's and 190's; why can't 20 wt oil?
Lowering kinematic viscosity at 100C from high viscosity grades while keeping viscosity index nearly constant is mostly done by making the base oils less viscous and therefore more volatile. High volatility becomes an issue.
Bruce can't go below a (something in the range of) 4cst basestock since volatility jumps to 30%. He can take the same basestock and easily bring it into a 20 range (has a hard time not doing it). That's why his 0w-10 only has a 150VI. If he tweaked it up to 8.2, in one manner or another, it would probably be in the 170+/- range ..or so I reason.
You're closer to the floor of sensible blending.
What is better?
There is no better. I guess a higher number is more impressive from a technology standpoint. But a lot of people seem to think that a lower VI is more stable.
Then they'd be wrong.
Well, sorta. Traditionally, high VI has been susceptible to degradation because it required tons of VI improvers. Nowdays, the VI improvers themselves are more stable and fewer are required because of higher VI base oils.
What I'm saying is that VI and 'stability' are two different things that used to appear to go hand in hand solely because of the limits of technology.