Trying To Understand VI

[Oil Changer]

Using analogies...

I have 170 dollars. You have 200 dollars. I think, big deal, you have 30 more dollars.

When I read brand X has a VI of 170 and brand Y has a VI of 200, should I be thinking wow, thats alot or should I think wow, big deal?

Is brand X having a VI of 170 and brand Y having a VI of 200 like driving from Detroit to Chicago or is it like driving from Detroit to LA?

Put yet another way, at what point should my ears perk up when reading different PDS on an oil's stated VI when trying to do a comparison?

 

[Food Scientist]

Should focus less on the paper stats and more on how well it performs in your vehicle (aka used oil analysis).

 

[Oil Changer]

Just trying to learn about VI, but thanks for the advice.

Nothing wrong with understanding what it is I am reading is there?

Using your example, what good would a used oil analysis do me if I was not able to interpret the results?

 

[ARCOgraphite]

DONT GET TOO CAUGHT UP WITH THE NUMBERS, The advertised VI are only good on new oil and will be much lower after 2k miles. Same with mRV. I would spend some time on the WIDMAN site and plug some numbers in. But VI vary basically mean that any grade oil with a high VI munber will be thinner (less viscous) at ambient starting temps than one with a poorer VI. Like 11/54 cSt @ 100C/40C - a high VI; versus 11/69 cSt - a middling VI.

 

[jstutz]

maybe to get a feel for its effects, find a calculator that plots viscosity over temp based on VI and a given viscosity. Then you could leave the viscosity the same and vary VI to see its effects in your range of interest. Looks like Widman you can put in one temp viscosity, then VI and get the other temp viscosity, then take those two numbers and plot with the other calculator. If you repeat this then you will see the projected effects of VI. I wrote a calculator that might help you visualize. Check it out and if i can modify it somehow to be more useful i will try to update it.

https://docs.google.com/open?id=0B6pXF6fWrLrgYjFlNmM0ZmMtODhhNi00ZmYwLWE3MmEtM2MyMTc3MjQ2ZDVk

 

[Oil Changer]

Thanks to those who have responded.

I knew this would be difficult, that is why I asked using analogies.

If I have a dollar and you have a million dollars, that is a big difference.

Basketball... the sun. Big difference.

Hardball... softball. Not a big difference.

Brand X claims a VI of 170. Brand Y claims a VI of 200. Should I think, MAN, that's HUGE! How the heck they do that?!? Or should I think to myself, big deal, 30 points, there's far more important stuff to worry about.

I think a true BITOG'er would know when and when not to raise an eyebrow over a published figure. That's all I want to know.

I know when someone says brand X has 100 ppm moly and brand Y has 1000 ppm moly there would be all sorts of excitement on the board. Just trying to figure out the same thing with VI instead of (for example) moly.

I don't know how else to ask.

 

[Rand]

well to answer your question.. its complicated.

and depends on how much of the VI is from VII's and how much is from basestock. And also how important fuel mileage is to you.. and your climate.

also there are different types of moly.

some are much more effective than others..

so brand A with 200PPM might be better than brand B with 400PPM.

Also VI isnt as big a deal in the summer. Its much more important when your nights are getting down to 0F etc.


Then you add in the fact that VII's shear and its like you are saying

I got a quarter to play this pinball machine. Is rewiring it important? this kind of stuff does not really lend itself to analogies very well.

 

[bepperb]

To give some perspective, after Crude is refined into (basically obsolete) group 1 oil it has a viscosity index of 100~110. Group 2 oils have an index of 110~120 maybe a bit higher. A group 3 might be 120~130 but probably not a lot higher than that. So that's your baseline.

Most oils will make some jump in VI by use of viscosity index improvers which aren't shear stable and don't last. Other oils might use a group 4 or 5 base that has a naturally higher VI.

So the big deal, if we assume a high VI is a desireable trait, is that they are achieveing this often without any viscosity index improvers.

 

[webfors]

Originally Posted By: Oil Changer
If I have a dollar and you have a million dollars, that is a big difference.

Basketball... the sun. Big difference.

Hardball... softball. Not a big difference.

Brand X claims a VI of 170. Brand Y claims a VI of 200. Should I think, MAN, that's HUGE! How the heck they do that?!? Or should I think to myself, big deal, 30 points, there's far more important stuff to worry about.


Answer: Big difference when it's -40 outside, not a big difference when it's +40.

 

[A_Harman]

To Oil Changer: See how there are no simple answers on BITOG?

We tend to begin our answers with "It depends..."

Out of all the responses so far, I like Rand's the best.

I prioritize my oil selection for my vehicles in the following order:
1. HTHS appropriate for recommended viscosity
2. Anti-wear content
3. Low NOACK, (or High Flash Point as a substitute)
4. Shear stability
5. Viscosity Index

I'm not as staunch an advocate for high VI as Caterham is, but for modern synthetic oils, VI below 155 is starting to be regarded as sub-par. VI's above 170 are respectable, and VI's above 200 are excellent. That's my sense derived from reading a lot of posts on BITOG.

 

[NateDN10]

To answer your question directly, here are some oils and their VIs. It'll give you a starting point at least.

Pennzoil HD30: 105
Pennzoil conventional 10w30: 135
Pennzoil conventional 5w30: 158
Pennzoil Platinum 5w30: 169

Note that this says nothing about how an oil performs in service, whether or not VI improvers are used, etc. It's just to give you an idea of the scale.

 

[Oil Changer]

Again, thanks for the responses. "bepperb" has came the closest to answering my question by assigning VI in relation to oil groups. My question to "bepperb" is, did you make those VI numbers up much like I did the 170/200 or are those numbers solid for each oil group? Is that really the expected VI for each group?

To be perfectly clear, I am NOT searching for an oil with the highest VI with the intent of using that in my vehicles because the high VI would make it the "best". I fully understand that would be as futile as searching for an oil that was "only PAO" and considering that the best oil for that reason alone.

I understand on an elementary level VI/VII. I thought the moly example would help but as noted, there are different types of moly that (when applicable) the higher moly count of one oil does not necessarily make it "better" depending on the type of moly used. And of course there is Ti...

CATERHAM likes (for his own reasons)Sustina (in part) due to it's (I'm assuming) very high VI of 229. He also likes (for his own reasons) the Toyota oil (in part) for it's (I'm assuming) very high VI of what is it 216 or 219, something like that?

The Toyota oil has a VI of ~219 and the Sustina 229. Focusing strictly at the VI numbers and ignoring how they achieve those numbers and their effects, is that a HUGE difference or should I think, big deal?

Or should I just stop asking and be blissfully unaware if that 10 point spread is meaningful or not?

 

[Oil Changer]

Thanks again for the latest batch of responses. They are coming closer to what I was asking for.

I just thought that there would be a solid classification system where one could tell if an assigned VI would be low/medium/high much like how an oil's viscosity (grade/weight) has to fall in a certain window to be classified the grade it claims to be.

 

[CATERHAM]

Originally Posted By: bepperb
To give some perspective, after Crude is refined into (basically obsolete) group 1 oil it has a viscosity index of 100~110. Group 2 oils have an index of 110~120 maybe a bit higher. A group 3 might be 120~130 but probably not a lot higher than that. So that's your baseline.

Most oils will make some jump in VI by use of viscosity index improvers which aren't shear stable and don't last. Other oils might use a group 4 or 5 base that has a naturally higher VI.

So the big deal, if we assume a high VI is a desireable trait, is that they are achieveing this often without any viscosity index improvers.

GP I oils may have a VI less than 80
GP II a VI of at least 80
GP IIa a VI of 100 - 115
GP III at least 120
GP III+, VI's as high as 140.

The best VIIs used today, especially those with a low molecular weight are very shear stable. There is an advantage to including at least some polymer thickeners in any finished formulation that goes beyond increasing the VI of the base oils. Even some race oils use VIIs.

Oil_Changer you've asked a good question.
A VI as high as possible is the holy grail in a motor oil.
The reason is, even the lightest 0W-20 oil is still too thick even at during a "cold" start at 100F.

The difference between a 170 VI and 200 VI oil translates into the equivalent of a full SAE grade in terms of start-up viscosity which obviously is a lot.
To give an example, Mobil 1 0W-20 has a 173 VI and the Toyota 0W-20 hgas a 216 VI. The Toyota oil will be 35% at 0C and still 25% lighter at room temperature.

But there are technical issues in formulating a 200+ VI oil. They're expensive to make because they can only be made from expensive high VI GP III or better oils. Since you're using lighter base stocks than lower VI finished oils the NOACK can be higher and of course you are limited to how much VIIs can be used.
The good news is that the limited number of 200 VI oils available do not have an oil shear issue and can be used with confidence.

 

[ARCOgraphite]

Originally Posted By: CATERHAM
... A VI as high as possible is the holy grail in a motor oil.
The reason is, even the lightest 0W-20 oil is still too thick even at during a "cold" start at 100F.
"Too thick" to what consequence? - I see absolutely none in moderate climate. I postulate there will be no significant wear due to the oil not being at operating temp viscosity. And the fuel mileage hit will be due to cold start enrichment, cold trans fluid, cold coolant. Then you have group III and IV loss of traction and lubricity over lower groups and I see a major compromise to no benefit whatsoever to also-ran 0w20 lubricants.

 

[DrDusty86]

Don't I repeat do not use used oil analysis as a wear indicator and post it on this site. They "M1 fanboys" will tell you that a $20 is not useful when detecting engine wear after there are results that there ARE better oils than M1.

 

[Capa]

It's not just the Mobil fan boys that tell you that a $20 used oil analysis is very limited---common sense would as well.

 

[Solarent]

Again CATERHAM delivers another clear explanation.

I would only add that the official definition of Viscosity index, or the VI (From the ASTM) is a measure of a loss of viscosity with increasing temperature.
Higher VI as Caterham has indicated means less loss in viscosity over temperature change, and when comparing them should be done via percentage change (so a VI 200 will change about 15% less over changes in temperature than a VI of 170). However as temperature approaches + 40 degress and oil becomes thin this difference is basically nullified.

IMO the VI of base oil is more important during formulation than the VI of the finished oil (which may or may not use VII - whether good ones or bad ones). However, it is important enough of a characteristic that it is part of what defines base oils from GR I, II, III etc, as well as sulfur content.

 

[Mitch Alsup]

Originally Posted By: ARCOgraphite
"Too thick" to what consequence? [/quote]

To thick to start the car, back out the driveway, and floor the motor entering the expressway.

But back to the original question. VII is simply a number that represents the quotient of another pair of numbers. Those other numbers are much more useful in understnading oil and lubrication than the VII number.

If we labled oil by actual viscosities instead of grade weights the picture would be more clear. Then one could actually look for an oil that was 10 cSt at 240dF where his engine runs.

 

[CATERHAM]

Originally Posted By: ARCOgraphite
Originally Posted By: CATERHAM
... A VI as high as possible is the holy grail in a motor oil.
The reason is, even the lightest 0W-20 oil is still too thick even at during a "cold" start at 100F.
"Too thick" to what consequence? -

The lightest 0W-20 oil available (Sustina) has a KV40 of 32cSt.
That's still too thick to use high rev's without the oil pump going into by-pass mode until the oil temp's are at least up to 65C or so. Not a big deal on the street when you can wait for the oil to heat up, but it is a big deal in situations where you can't wait you the oil to reach normal operating temp's before using maximum rev's.
Racing is a good example, and M1 R 0w50 has a 189 VI.