Mobil 1 (Australia) viscosity indices.

[crinkles]

I found it interesting that Mobil 1 10w30 down here has a low VI of 147.
5w30, has a VI of 169

0w-40,0 has a VI of 186

is the viscosity index an indicator of a "better" oil? i don't thin it is , as I understand the way the oil viscosity decreases with increasing temperature is described by it.

Then again i've heard that high quality synthetics usually have a higher VI. or is this baloney?

 

[XS650]

Short answer = no.

If all you know is the VI and not how it was achieved, you can't draw any conclusion about the quality of the oil.

Here's some fuzzy statements that illustrate the difficulty of giving you a concise answer.

If the high VI was achieved with VI improves, then the high VI oil is not as robust as a lower VI made oil with from the same base stock.

If you have two oils, made from different base stocks, each with the same amount of the same type of VI improver (possibly none), then the one with the higher VI stands a good chance of being better oil.

 

[crinkles]

clear as mud, bud!

i get what you're saying.

in effect i'd be foolish to judge Mobil 1 10w30 an inferior product tot he Mobil 1 5w30 solely on the VI. FWIW the 5w30 is thicker at both 40 deg C and 100 deg C in our formulations.

 

[Shannow]

crinkles,
given the information that you've provided in isolation, and as the only information available (other than they were M1 synthetic), I'd be more inclined to choose the 10w30 over the other two.

Knowing the 0W-40s global position would change my answer.

 

[gwdriver]

crinkles- I really like your part of the planet. When I was a pilot in the military I flew to Christchurch, Richmond , and Alice Springs twice a week. In our American formulations Mobil 1 10w30 is also thinner than their 5w30. Weird huh!

 

[CATERHAM]

There is no question, the higher the VI the better.
Syn oils have naturally high VI's, with certain GP IV & V better than others.
Obviously, the broad range multi-viscosity oils such as 0W-40, 5W-50 and 10W-60 have a significant amount of VII in their formulations. And some VII are more shear stable than others.

Using your M1 example. Their 10w30 oil has little if any VII. It also has a lower 100C vis (10 cSt vs 11.3 cSt) than their 5w30 but still has a higher HTHS vis. But the 10W has a higher vis at start-up due to it's lower VI. The 5W is not as shear stable over long OCI's.
So as you can see it's not that straight forward to call the 5W
a better oil than the 10W based on it's higher VI alone.
But it is certainly an important metric to keep in mine when choosing any oil.