Determining the REAL V.I. of a motor oil

[KrisZ]

Originally Posted By: TrevorS
Originally Posted By: OVERKILL
Originally Posted By: TrevorS
No it's not the same thing.

How a metric is calculated affects its interpretation. That's what this alternative method is about.


Right, but its still a metric calculated off of only two data points.


The point is that calculating it the way CATERHAM did gives a different way to compare oils which for the purposes if understanding VI is arguably better than the old way.


Hold your horses... Not too long ago VI was pretty much the most important metric to Catheram and many jumped on board blind folded. Many of us questioned the reasoning and got a lot of flak.
Now you're proclaiming that this new ratio is "arguably better than the old way" without fully understanding the issue here.

This is just a ratio and the whole premise of Catheram looking first at VI number and now at this ratio if to have some sort of a "meaningful" number that one can go by without much thinking. With VI the higher the number, the better, with this ratio the lower, the better.

The real question here is; How meaningful is such a number?

 

[jake88]

Glad everyone is starting to think about the limitations of the VI method. Not that it is a useless number, but the temperatures chosen are arbitrary and there are just many more measures that we could be using rather than kinematic viscosity.

You could conceive of all kinds of better numbers - how about a measure which compares the HTHS performance of an oil at multiple temperatures??

 

[Garak]

Originally Posted By: OVERKILL
Right, but its still a metric calculated off of only two data points.

Absolutely, but that is one more data point than we are typically given. KV40 and KV100 are measured the same way. Caterham's ratio idea just takes away some of the constants used in the calculation. It would be nice if we had a KV0 and a KV(-20) and so forth to compare. And we can't readily compare HTHS to KV to MRV.

With viscosity being non-linear, only so much can be done. All that VI is trying to show is how much viscosity shifts over a relatively narrow range of temperatures. We can't expect miracles out of it.

Generally speaking, a higher VI type oil is preferred. I just don't think it's necessary to get overly hung up on how that index is calculated or determined. I know that an SN/GF-5 5w-30 should have a higher VI than an SN/GF-5 10w-30, making the 5w-30 generally preferable. Whether the difference in VI is 20 points or 50 points doesn't matter a great deal to me.

As I've stated before, I'm not hunting for the highest VI example of my chosen viscosity. Nonetheless, a very poor VI will disqualify an oil choice.

 

[OVERKILL]

Originally Posted By: TrevorS

This does not mean VI is important or the underlying data points are the best. Just that given we have that data, if were going to interpret it with a metric called VI, this method is potentially more meaningful.


That's entirely my point. I feel like we are painting a turd gold here

Not that the turd may lack any semblance of usefulness of course. But painting it gold certainly doesn't inherently ascribe more value to whatever that usefulness may be.

For the last while we have been told repeatedly that VI is one of, if not THE most important characteristic of an oil. Now that's done almost a complete 180. For those that worship at the house of VI, that's like finding out their golden idol is paint over cardboard.

For those of us who would rather reference CCS, MRV and HTHS as indicators as to an oil's performance from cold to hot, this entire thing would seem to lend merit to that being a far better metric and falls in-line with what Shannow has stated above.

 

[Garak]

I don't think Caterham, for instance, has much objection to the use of MRV and HTHS, except, with in regards to the former, so few people actually experience such low temperatures and he pays attention to HTHS. BTW, it's -32 C here right now. I have no idea what the heck is going on lately!

I think we have to take VI for what it's worth. It's certainly not useless, but it does have its limitations. High VI doesn't guarantee a 0w-XX oil, nor does a 0w-XX guarantee a ultra-high VI. In the end, lubrication engineers have always been trying to minimize changes in viscosity as temperature changes, and that's the lesson here.

 

[Solarent]

Originally Posted By: CATERHAM
So I got to thinking, how can we avoid the V.I. penalty that applies to lower viscosity oils and determine the "REAL V.I." regardless of how thick or thin an oil actually is?
One method that does avoid this problem occurs when an oil's viscosity that's based on the same KV40 and KV100 spec's used to calculate it's ASTM V.I. are plotted on a graph commonly used in viscosity calculators. When you graph oils with different viscosities you are comparing the oil's "REAL V.I.".
But what we need is a "REAL V.I." number to replace the ASTM V.I. number. What better than using a ratio of KV40/KV100? We could also use the reciprocal but I think whole numbers are more insightful than fractional numbers.


Lets not get too far ahead of ourselves here. The article in question discusses VI in relationship to base oils not finished oils. There is an important difference here because base oils are influenced by feedstock and refining techniques whereas finished oils are influenced by formulation choices.

that's why I said this in the original thread regarding a finished formula's VI:
Originally Posted By: Solarent
A word of caution: be careful trying to predict an oil's viscosity at extremely cold or extremely hot temperatures using the VI as a reference. Because the VI is a calculated number, which uses a somewhat arbitrary formula, you can get widely different results due to the differences in formulas of the finished oils. Most online calculators can give an estimate, but this may vary because the components of the finished oil's formula may be designed to produce a specific result, not just based on the calculated VI.


When selecting the viscosity performance necessary for your engine you should look at all the viscosity performing specifications: VI, HTHS, MRV, CCS and the two KV references; choose the one that meets the most of your target requirements and don't forget the importance of other performance characteristics and the additives used in the formula.

 

[OVERKILL]

Originally Posted By: Solarent


When selecting the viscosity performance necessary for your engine you should look at all the viscosity performing specifications: VI, HTHS, MRV, CCS and the two KV references; choose the one that meets the most of your target requirements and don't forget the importance of other performance characteristics and the additives used in the formula.

Great post

 

[TrevorS]

Don't forget that MRV and CCS can be irrelevant to many people while highly relevant to others.

For me they are not relevant unless I'm missing some interpretation about what implications they have for starts between 10c and 25c.

 

[OVERKILL]

Originally Posted By: TrevorS
Don't forget that MRV and CCS can be irrelevant to many people while highly relevant to others.

For me they are not relevant unless I'm missing some interpretation about what implications they have for starts between 10c and 25c.


Well, they imply how much an oil thickens as it gets very cold

How that works in creating a slope from say 40C, well?

Wouldn't a great data point be 0C? You could plot from CCS to 0C to 40C then to 100C and get something of a decent looking curve reflecting the lubricant's true behaviour.

 

[CATERHAM]

Originally Posted By: Solarent
Originally Posted By: CATERHAM
So I got to thinking, how can we avoid the V.I. penalty that applies to lower viscosity oils and determine the "REAL V.I." regardless of how thick or thin an oil actually is?
One method that does avoid this problem occurs when an oil's viscosity that's based on the same KV40 and KV100 spec's used to calculate it's ASTM V.I. are plotted on a graph commonly used in viscosity calculators. When you graph oils with different viscosities you are comparing the oil's "REAL V.I.".
But what we need is a "REAL V.I." number to replace the ASTM V.I. number. What better than using a ratio of KV40/KV100? We could also use the reciprocal but I think whole numbers are more insightful than fractional numbers.


Lets not get too far ahead of ourselves here. The article in question discusses VI in relationship to base oils not finished oils. There is an important difference here because base oils are influenced by feedstock and refining techniques whereas finished oils are influenced by formulation choices.

that's why I said this in the original thread regarding a finished formula's VI:
Originally Posted By: Solarent
A word of caution: be careful trying to predict an oil's viscosity at extremely cold or extremely hot temperatures using the VI as a reference. Because the VI is a calculated number, which uses a somewhat arbitrary formula, you can get widely different results due to the differences in formulas of the finished oils. Most online calculators can give an estimate, but this may vary because the components of the finished oil's formula may be designed to produce a specific result, not just based on the calculated VI.


When selecting the viscosity performance necessary for your engine you should look at all the viscosity performing specifications: VI, HTHS, MRV, CCS and the two KV references; choose the one that meets the most of your target requirements and don't forget the importance of other performance characteristics and the additives used in the formula.

Yes the article pertained to base oils but the problems I high-lighted with ASTM D2270 also very much apply to finished oils.
One of the criticisms of V.I. is that it is a dimensionless number. The KV40/KV100 ratio which is the rate of viscosity change with temperature that ASTM D2270 is based on, gives it some real meaning.
We have learned that a 200+ V.I. oil is is a very high V.I oil and it is with 20 grade oils meaning that it's viscosity change with temperature has been minimized but it's not in real terms if we apply that same ASTM V.I. 200+ V.I. to 40 or 50 grade oils not that there are many that have a V.I. that high. But even if they could (Sustina 0W-50 notwithstanding) they still would not have a high real V.I.
And that is the main point of this thread as most members don't realize that.

As to your point regarding what viscosity spec's to consider in choosing an oil. MRV and CCS have no relevance in most applications and that even applies to most Canadian like myself. But for the few that are routinely starting their cars unaided at temp's of -30C and colder, not much else does matter.
I've mentioned this many times but at normal operating temp's the single most important viscosity spec' is HTHSV followed by my an oil's V.I.

The importance of an oil's real V.I. is not just about being relatively light at typical start-up temp's which I appreciate is not particularly important to many although I wish more would install oil pressure gauges and that might change their minds but that's a separate issue. It's important at very hot oil temp's because the higher the V.I. the greater the high temp' protection should oil temp's continue to rise.
That's why the most advanced race oils have high V.I.'s and a 0W rated. The 0W rating of course has nothing to do with a desire to pump at -40 degrees but rather is a by-produce of choosing high V.I. low viscosity base oils.

 

[Shannow]

VI, calculated the way that it is gives various viscosity basestocks from particular high quality crudes an index of 100...and parallel lines on the log vis/temp curve.

That's what the metric was created for, not to "penalise" TGMO 0W-20 for being too thin.

These oils are thinner at 40 than their counterparts, on the simple metric of KV40, that much is obvious to anyone...why rejig VI to make them "look" better when that wasn't the purpose of the original calc???

 

[Solarent]

Originally Posted By: CATERHAM
We have learned that a 200+ V.I. oil is is a very high V.I oil and it is with 20 grade oils meaning that it's viscosity change with temperature has been minimized but it's not in real terms if we apply that same ASTM V.I. 200+ V.I. to 40 or 50 grade oils not that there are many that have a V.I. that high. But even if they could (Sustina 0W-50 notwithstanding) they still would not have a high real V.I.

Can you clarify this statement a bit?
The reason I am asking is because lets say you take two hypothetical oils:
0W20 with VI of 200 (target kv.100 5.6-9.3)
0W50 with a VI of 200 (target kv.100 16.3-21.9)

Both will have fairly minimal viscosity change with temperature (the same rate of change as they have the same VI) but the target KV @ 100 will be different (this is what gives it the SAE 20 or SAE 50 rating) Remember, the lowest possible SAE grade for an oil is the one that must be represented on the bottle, this is the main reason besides a complete lack of need you don't see mainstream 0W50 oils.

Therfore if you were to plot their viscosities on a graph (Kinematic viscosity plots on a log scale against temperature on a linear scale to produce a linear relationship.) the slope of the line would be the same, but the placement would be different.

 

[MolaKule]

I really don't see what these ratios buy us.

VI is a mathematical, non-dimensional construct that gives us a rough, but not complete, description of oil viscosity at two temp measurements.

 

[OVERKILL]

Originally Posted By: MolaKule
I really don't see what these ratios buy us.

VI is a mathematical, non-dimensional construct that gives us a rough, but not complete, description of oil viscosity at two temp measurements.


It makes the "high VI" 0w-20 oils look even more awesome

That's about what I take away from it.

 

[CATERHAM]

Originally Posted By: Solarent
Originally Posted By: CATERHAM
We have learned that a 200+ V.I. oil is is a very high V.I oil and it is with 20 grade oils meaning that it's viscosity change with temperature has been minimized but it's not in real terms if we apply that same ASTM V.I. 200+ V.I. to 40 or 50 grade oils not that there are many that have a V.I. that high. But even if they could (Sustina 0W-50 notwithstanding) they still would not have a high real V.I.

Can you clarify this statement a bit?
The reason I am asking is because lets say you take two hypothetical oils:
0W20 with VI of 200 (target kv.100 5.6-9.3)
0W50 with a VI of 200 (target kv.100 16.3-21.9)

Both will have fairly minimal viscosity change with temperature (the same rate of change as they have the same VI) but the target KV @ 100 will be different (this is what gives it the SAE 20 or SAE 50 rating) Remember, the lowest possible SAE grade for an oil is the one that must be represented on the bottle, this is the main reason besides a complete lack of need you don't see mainstream 0W50 oils.

Therfore if you were to plot their viscosities on a graph (Kinematic viscosity plots on a log scale against temperature on a linear scale to produce a linear relationship.) the slope of the line would be the same, but the placement would be different.

If your graph the your two examples out you will see that the 200 V.I. 0W-20 has a much more gradual slope than the 200 V.I. 0W-50.
The closest 0W-20 would be the Idemitsu made Honda 0W-20, KV40 39.94cSt and KV100 8.52cSt, V.I. 197 Ratio 4.66. Sustina 0W-50 has a PDS KV40 of 95.43cSt and KV100 of 17.29cSt, V.I. 204, ratio 5.52. Graph and you'll see there very different slopes.

Here's another example of the V.I. penalty that applies to lower viscosity oils from another thread:

Originally Posted By: dparm
Here's an example:

Mobil 1 0w40 has a VI of 185, and HTHS of 3.8
Red Line 10w60 has a VI of 187, and HTHS of 5.8


Despite having the same VI, the Red Line is nearly 35% thicker under normal use.

Remember that VI can be calculated based on the kinematic viscosity (KV) values, so two oils of vastly different viscosities can have the exact same VI. Don't believe me? Try the calculator for yourself:

CATERHAM's reply:
Actually RL 10W-60 is about 50% heavier than M1 0W-40 at 150C and M1 0W-40 is 35% lighter.
At 100C RL is over 90% heavier.
Why the disparity? Because the real V.I. of the two oils are quite different with M1 0W-40 being about 18% higher.
When comparing the real V.I. of two oils of different grades you have to take into account the V.I. penalty that applies to lighter oils.
The real V.I. of M1 0W-40 as represented by it's KV40/KV100 ratio is 5.56 meaning as the viscosity drops from 100C to 40C it increases 5.56 times. For RL 10W-60 it increases 6.54 times.

 

[Solarent]

This is why I said we shouldn't get too far ahead of ourselves.

You are attempting to describe the viscosity temperature relationship as if it is linear. It is not.

If you plot your two examples (Honda 0W20 and Sustina 0W50) on a KV log scale vs temperature linear scale (as I mentioned above and has been explained many times by those of us who do this for a living) you can then see them in a linear relationship. When you do this, with your examples, the lines become basically parallel on the graph separated by the difference in viscosity between the two grades. (the slight difference in slope is attributed to the difference in VI)

I agree with much of your advice on the importance of viscosity index when comparing oils with the same SAE grade, as well as the extensive work you have done on your own vehicles with regards to the benefits of understanding oil pressure, and the implications viscosity performance has on operating conditions. In this case though, I don't see where where your linear comparison of kinematic viscosity ratios can compensate for the perceived "VI Penalty" which was identified with base oils. This penalty as identified in the article has to do with predicted viscosity index and refining techniques. It has nothing to do with finished oils that use Viscosity Index Improvers. It's comparing apples to oranges in my books.

Here are some references for those interested:
HTHS from Lubrizol
Absolute and Kinematic Viscosity from Noria
Viscosity Basics from Chevron (Go through all the links on the left side to learn about viscosity grades and the tests that apply at different shear rates and temperatures).

This is why when evaluating viscosity performance for a single engine in a given set of conditions there is no one test which is better than the others, only the sum of the relevant ones to the conditions where the engine operates, which will give the most complete perspective.

 

[MolaKule]

Originally Posted By: Solarent
This is why I said we shouldn't get too far ahead of ourselves.

You are attempting to describe the viscosity temperature relationship as if it is linear. It is not.

If you plot your two examples (Honda 0W20 and Sustina 0W50) on a KV log scale vs temperature linear scale (as I mentioned above and has been explained many times by those of us who do this for a living) you can then see them in a linear relationship. When you do this, with your examples, the lines become basically parallel on the graph separated by the difference in viscosity between the two grades.

I agree with much of your advice on the importance of viscosity index when comparing oils with the same SAE grade, as well as the extensive work you have done on your own vehicles with regards to the benefits of understanding oil pressure, and the implications viscosity performance has on operating conditions. In this case though, I don't see where where your linear comparison of kinematic viscosity ratios can compensate for the perceived "VI Penalty" which was identified with base oils. This penalty as identified in the article has to do with predicted viscosity index and refining techniques. It has nothing to do with finished oils that use Viscosity Index Improvers. It's comparing apples to oranges in my books.

Here are some references for those interested:
HTHS from Lubrizol
Absolute and Kinematic Viscosity from Noria
Viscosity Basics from Chevron (Go through all the links on the left side to learn about viscosity grades and the tests that apply at different shear rates and temperatures).

This is why when evaluating viscosity performance for a single engine in a given set of conditions there is no one test which is better than the others, only the sum of the relevant ones to the conditions where the engine operates, which will give the most complete perspective.


Bingo!

 

[JAG]

I think what is essentially sought is the slope of the viscosity curve between 40C and 100C. I say to use the mathematical difference in viscosities and skip dividing that by the difference in temperatures, which is how slope would be calculated.

It's true that higher viscosity oils of the same "type" and with the same VI as thinner ones will thin at a higher rate between 40C and 100C. Not only is the ratio of viscosities (40C/100C) higher for the thicker oils but even more dramatic is the mathematic difference in viscosities. This is evident when looking at the algebra when calculating the difference, given the ratio. Simple example: thick oil ratio is 10 and the two viscosities are 100 and 10. Difference is 90. Thin oil ratio is 5, with two viscosities of 35 and 7. The difference is 28. So the slope of the thick oil's viscosity curve between 40C and 100C is roughly 3 times the slope of the thin oil's viscosity. This would not be immediately obvious when looking at VI or the ratio of viscosities at 40C and 100C.

VI was created for the reason that Shannow said. I can understand why someone would wanting a number, created from kv's at 40C and 100C, that tells you what you really want to know. What I think you are looking for would be nicely filled by simply taking the difference in viscosities at 40C and 100C. I hope this post is not a mess since I typed it on my phone.

 

[CATERHAM]

Solarent, the last thing I'm implying is a linear relationship between KV40 and KV100.
The ratio is just a number that does represent the real extent of the viscosity change with temperature.
Suggesting the V.I. penalty that applies to base oils doesn't also also carry over to finished oils is a very odd thing to say because it obviously does.

 

[Garak]

Originally Posted By: CATERHAM
Suggesting the V.I. penalty that applies to base oils doesn't also also carry over to finished oils is a very odd thing to say because it obviously does.

Regardless of whether or not that statement is correct, the only real solution would be for oil companies to publish actual viscosity curves on their data sheets for each oil, rather than VI values. I can't see that happening, though, and if we ask them, they'll think we're more nuts than they already do.