Which 20 wt oil has best Viscosity Index (VI)

pbm

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 Originally Posted By: CATERHAM
I'll give a head start: RLI 5W-20 is 179 RLI 0W-20 178 Motul 300V 0W-20 172 PP 0W-20 170 RL 0W-20 166
The problem with the oils that you have listed is that none of them are found in WM, PB, AA, AZ etc... They are all specialty oils. What about Mobil 1 0w20 and 5w20, PP 5w20, Synpower 5w20 etc...
 

CATERHAM

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M1 0W-20 VI not listed unless someone knows how to calculate from vis at 40C and 100C? M1 5W-20 is ......... 163 PP 5W-20 ....... 160 Valvoline Syn 5W-20 is 160 " .........0W-20 is 170
 
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 Originally Posted By: CATERHAM
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.
 

JAG

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 Originally Posted By: CATERHAM
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.
 
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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.
 

CATERHAM

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Jag, 0W-20 oils with VI's in the 170's appear to retain their viscosity very well in UOA, better than many 0W-30 and 0W-40 grades. I don't see any evidence of pushing the limit in any 0W-20 yet.
 
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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.
 
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 Originally Posted By: bepperb
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.
 
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