Determining the REAL V.I. of a motor oil

[Solarent]

Originally Posted By: 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.


By dividing the KV40/KV100 to get the ratio you describe and then using that ratio to compare finished oils with a widely different viscosity range you are implying a linear relationship. This can be solved very simply by comparing a kv linear scale graph vs temperature to the kv log scale vs temperature graph I described.

The reason I stated that the VI penalty as described in the article doesn't apply is because to say it does would negate the impact of viscosity modifiers which are one of the primary ingredients to achieving the finished formula's viscosity performance.

 

[JAG]

Quote:
The reason I stated that the VI penalty as described in the article doesn't apply is because to say it does would negate the impact of viscosity modifiers which are one of the primary ingredients to achieving the finished formula's viscosity performance.

I don't think anyone here would disagree that viscosity modifiers play a huge role in finished lube viscometrics. I think the point is that the reference oil for the VI calculation is different than the reference oil for 0W-20 oil and as a result, comparing their VIs is a bit like comparing oranges and lemons. That is, even if they had the same VI, they will not have anywhere near the same slope on their viscosity curves (on linear-linear scales) between 40C and 100C.

 

[Solarent]

Originally Posted By: JAG
That is, even if they had the same VI, they will not have anywhere near the same slope on their viscosity curves (on linear-linear scales) between 40C and 100C.


This is true, which is why we don't use linear-linear scales when discussing Viscosity Index. If you convert to a kv(log)-linear scale as has been explained then the slope evens out.

When comparing viscosity performance, using the VI with oils within the same grade can be a good way to compare them. You just can't stretch this outside of the grade or to somehow justify that 0W20 is going to be better than 5W30 in every instance just because it has a higher VI. Similarly the calculated ratio CATERHAM has proposed is no more helpful in comparing oils with different grades than VI is.

This is why you must take a look at all the viscosity properties as they apply to you and not focus solely on one attribute (even if it is a very important one).

One of the key points in the article is to not make judgements about an oil's quality based solely on VI. I agree 100% with that statement - even though the entire article is about base oils, I think that principle is sound with finished oils as well.

 

[Shannow]

I still don't get how the lower viscosity basestocks are "picked on" by V.I...

100 was chosen as the number that the (best) of the solvent refined basestocks, from the same source in the day performed, they were parallel lines when mapped on the logarithmic scale that matched the viscosity curves of all of the grades of oil.

Surely it seems reasonable that stocks from the same oil are considered "the same" regardless of grade, and before modification.

It makes less sense to make a new VI/ratio that gives all Pennsylvania crude solvent extracted grades different "VI/ratios"

 

[CATERHAM]

Originally Posted By: Solarent
Originally Posted By: 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.


By dividing the KV40/KV100 to get the ratio you describe and then using that ratio to compare finished oils with a widely different viscosity range you are implying a linear relationship. This can be solved very simply by comparing a kv linear scale graph vs temperature to the kv log scale vs temperature graph I described.

The reason I stated that the VI penalty as described in the article doesn't apply is because to say it does would negate the impact of viscosity modifiers which are one of the primary ingredients to achieving the finished formula's viscosity performance.

You've got the "cart before the horse" as my late father would often say.
When you apply the KV40 and KV100 spec's to a viscosity calculator and plot out the results you are avoiding the V.I. penalty that's built into the ASTM D2270 V.I. calculation.
That is my main initial premise.
Bringing VMs into the discussion is immaterial as it would only affect interpolation and extrapolation in predicting other viscosities, the KV40 and KV100 are actual viscosity measurements.
Taking the KV40/KV100 ratio not only tells one exactly how much the viscosity changes between those two temperatures, something the ASTM V.I. does not, but it allows one to compare the real V.I.'s of different oil grades.

 

[Shannow]

For crying out loud...the KV 40 tells you what it is at 40, and the KV100 what it is at 100. You have the data that you apparently need, without a new dimensionless number which means squat without either a KV100 or KV40 to fix one end of it.

VI was for basestock comparison only in it's initial form, playing with it to compare finished oils is silly...

 

[OVERKILL]

Originally Posted By: Shannow
For crying out loud...the KV 40 tells you what it is at 40, and the KV100 what it is at 100. You have the data that you apparently need, without a new dimensionless number which means squat without either a KV100 or KV40 to fix one end of it.

VI was for basestock comparison only in it's initial form, playing with it to compare finished oils is silly...


I think I'm going to come up with my own new "real VI" formula using CCS and KV40 and then I'll laud it as the only true way to know an oil's start-up and cold start performance

 

[Solarent]

Originally Posted By: CATERHAM

When you apply the KV40 and KV100 spec's to a viscosity calculator and plot out the results you are avoiding the V.I. penalty that's built into the ASTM D2270 V.I. calculation.
That is my main initial premise.

I understand that this is your premise, what I am saying is that your reasoning is flawed.
When you plot it out properly (using the logarithmic scale) the VI system works fine, and there is no need to create your own system.

There is a big difference between absolute viscosity and kinematic viscosity (read the Noria article I posted earlier). They respond differently to temperature once Viscosity Modifiers are included. That's why you can't apply research intended for base oils directly to finished oils.

Originally Posted By: CATERHAM

Taking the KV40/KV100 ratio not only tells one exactly how much the viscosity changes between those two temperatures, something the ASTM V.I. does not, but it allows one to compare the real V.I.'s of different oil grades.


Can you please explain what you mean by the "real V.I." ?
In what way is it any different or better than the current VI system for finished oils?

 

[Shannow]

Originally Posted By: Solarent
Can you please explain what you mean by the "real V.I." ?
In what way is it any different or better than the current VI system for finished oils?


I'll ask the OP to review these two data sheets for two finished ranges of products, and tell us what more the "new real" VI system will tell us about the make-up of the products.

http://www.mobil.com/Australia-English/Lubes/PDS/GLXXENCVLMOMobil_Delvac_1330_1340_1350.aspx

http://www.mobil.com/USA-English/Lubes/PDS/GLUSENCVLMOMobil_Delvac_1600_Monogrades.aspx

Specifically how it would ADD rather than subtract from the knowledge contained in the data sheet...

 

[supercity]

Originally Posted By: CATERHAM

But my point is not about that, but rather on how ASTM V.I. is measured and the penalty that's applied to low viscosity oils.
The example I gave was that M1 0W-40 with it's 185 V.I. is reality no higher than a 160 V.I. 5W-20. There are no high V.I. 40 grade and heavier oils.



What penalty are you referring to? You can cross out the manufacturer's VI score and replace it with whatever you like, it won't change the product.

 

[dparm]

As always, we need to careful not to put too much weight on a single piece of data. I think we tend to get too fixated on certain numbers: VI, HTHS, TBN, NOACK, etc. While these are all useful in different ways, it is the overall package that matters most. I think we've seen enough UOAs on here to agree that many oils appear rather mediocre on paper but perform quite well in service. The opposite has also held true: oils look fantastic on a manufacturer spec sheet, but don't really live up to expectations.

I think this is still interesting and thought-provoking, but I want to caution other readers not to weigh their decision solely on one or two line items in a datasheet.

 

[Boxnuts]

The VI calculation does produce some curious figures. If we take it to the extreme and calculate (using Widman) the VI for "perfect" oils i.e. oils that have the same viscosity at 40°C as at 100°C. We get.
A 20cst oil has a VI of 874
A 5cST oil has a VI of 1647.

If the VI calculation was what I would call sensible then the VI's above would be the same. But they are not, so it's clearly not a very sensible system. What I'm not sure about is why the low viscosity oils are said to "penalized". As the above figures show it is easier for a low viscosity oil to get a high VI. Define penalized.

 

[AEHaas]

I think that no technical data whether dynamic or calculated is valueless. The more you know the better you can decide on what is best for your particular application.

Scientific studies, even at the most basic level, may have something that helps with Your analysis. Even poorly designed studies with wrong conclusions may be useful when you look at the actual data.

As already stated, picking an oil involves looking at all of its properties, not just viscosity as most seem to be stuck on. I’m with Shannow that some of the most important numbers for Me are the KV 40 and 100. These tell me most of what I need to know about the viscosity for my applications.

Overlooked in this discussion is another dimension in your decision tree. What happens when you use a particular oil in your car? What does your car tell you about your oil choice? Do you tear apart your filter, how about a blot test, are you getting a full and proper analysis of your used oil, it’s color, the pressures and temperatures of our engine and oil, et cetera?

I am very comfortable with the oils I have used based on all of the above.

My current experiment is that I am running Motorcraft 5W-20 semi-synthetic oil in my wife's Lamborghini (do not tell her - she has not noticed any difference since the RLI was dropped out of the pan).

aehaas

 

[benjy]

always reading to learn, on theoilevaluators they mention how some specs being easily "propped up' + viscosity index being one. also stated generally an oil with less VII will have a better HTHS, also noted is specs are for NEW oils + some that use lots of cheap additives can degrade quite quickly

 

[Garak]

What is a "better" HTHS? Is it "better" if it's higher or lower? "Better" when referring to something like HTHS is simply a weasel word.

 

[Shannow]

IMO, and apparently in the minds of the SAE J300 committees
a) when they introduced HTHS due to the failings of VII enhanced oils in the '70s; and
b) when they moved the minimum HTHS to 3.5 for 0W, 5W, and 10W 40s from their previous 2.9

"Better" in that context means that the KV150 and the HTHS (150) should be close together if possible...i.e. we have the lowest temporary shear under high shear rates.

We don't have a KV150 available to us generally, nor the High Shear 100 (the supertech 5W30 datasheet being a welcome exception)...so we have to use KV100 and HTHS.

Take a "40" (straight) of 12.5 KV100. A "newtonian" fluid, of VI 100 (as was traditionally the "good oil" that was available in Pennsylvania), and it would have an HTHS of around 4.5/4.6.

So the KV100/HTHS would be 12.5/4.5 = 2.78, (at the top end of 40 grade, 16.3CST/5.8 = 2.8 also)...incidentally, a 20 of VI100, had about the same ratio, and an 8.5cst 20 would have had an HTHS of around 3...


While the pre 2013 10W40 was allowed an HTHS the same as the minimum for a 30, the ratio would be 12.5/2.9 = 4.3, up to 5.6 for top of KV100, minimum HTHS...the latter had a much better VI than the former, but much greater temporary shear.


...the post 2013 10W40 can, at worst, with the top end of KV100 and minimum HTHS of 3.5 only be around 4.6. So with the same VI, can have a lubricant with less temporary shear (i.e. more predictable, natural if you will...allows easier design, as the oil behaves closer to the same at normal and high shear rates, less pumping losses at low shear when HTHS is the protector of things bearing and the like)...

it's reflective of better VIIs becoming available, but also demonstrates the folly of chasing VII at the expense of temporary shear.

"Better" isn't more, or less...it's "closer to the newtonian" for the KV150 and the HTHS.

 

[userfriendly]

The HTHS of SAE 20 went up a little with the last J300 revision as you know.

I like the 40C number on the spec sheet and the specific or API gravity as well.

Just for interest sake if nothing else.

Since I only buy finished lubricants and not base oils, the specification on the package
is good enough for me.

For example, 5W40 CJ-4/SN tells me more about the product than all the other specifications
combined.

What surprised me is how similar all the base oils are in VI, irregardless of their grade.

The group 2s around 100-105, and the 2+ and 3s all about 110-125.

I have two questions;

1. Someone said that pour point is not a very good indicator of a lubricant's
suitability for a low temperature application.
Is that true?

2. How much fuel could I save in a year if I drove with one headlight burnt out?

 

[Shannow]

from my library...1993 still had 2.6 hths for the 20s

 

[riggaz]

Originally Posted By: CATERHAM
The October issue of LUBES'N'GREASES had an excellent article by Dr. Jack Zakarian, titled
"V.I. Too Resistant to Change" that was captioned and discussed in the following post:

http://www.bobistheoilguy.com/forums/ubbthreads.php/topics/3148253/1

The gist of the piece was that Jack Zakarian was quite critical of the method detailed in ASTM D2270 by which the V.I. of an oil is calculated.
He summarized as follows:
"ASTM V.I. does not accurately represent the "real V.I." of oil .... the rating method suffers from a number of inconsistencies that penalize lower viscosity oils compared to their higher viscosity counterparts. In addition, V.I. has no fundamental relationship to the true viscosity-temperature behavior of an oil, even though it is widely presumed to have one. At best, V.I. ia a very rough guide to viscosity-temperature behavior.
By understanding the deficiencies in the rating method, users will be better able to interpret and understand the actual V.I. numbers."

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.

For example M1 0W-40 (ASTM V.I. 185) has a KV40/KV100 ratio (75cSt/13.5cSt) of 5.56, meaning it's kinematic viscosity increases 5.56 times as the temperature drops from 100C to 40C.
M1 5W-30 (V.I. 172) has a ratio (61.7/11.0) of 5.61.
M1 0W-20 (V.I. 173) has a ratio (45.8/8.7) of 5.26.
Although the lighter M1 5W-30 has a significantly lower ASTM V.I. it's viscosity change with temperature ratio is only slightly higher and the even lighter 0W-20 actually has a lower ratio or a higher "REAL V.I." to M1 0W-40. That is an example of the V.I. penalty that applies to lower viscosity oils that Dr. Zakarian was referring to.

Just for fun, I've ranked a bunch of oils based on their KV40/KV100 ratios representing their "REAL V.I.'s" from the lowest to the highest:

Joe Gibbs XPO 0W-5, race oil, PDS spec's - ASTM V.I. 170, 11.5cSt/3.3cSt = 3.48
RL 0W-2, race oil, PDS spec's - V.I. 136, 11/3 = 3.67
Marvel Mystery Oil, PDS & VOA - V.I. 96, 10/2.64 = 3.79
Sustina SN 0W-20, PDS - V.I. 229, 32.69/7.94 =4.12
Mazda Moly SN 0W-20, VOA - V.I. 221, 35.85/8.37 =4.28
TGMO SN 0W-20, VOA - V.I. 216, 37.4/8.5 = 4.38
Motul 300V Sprint 0W-15, VOA - V.I. 155, 23.3/5.1 = 4.57
Honda (Idemitsu) SM 0W-20, PDS - V.I. 197, 40/8.5 =4.66
TGMO SN 0W-20/M1 SN 0W-20, 60/40 0W-30 blend, PDS - V.I. 203, 48.9/10.2 =4.79
Sustina SN 5W-30, VOA - V.I. 194, 51.5/10.3 =4.99
PP SN 5W-20, PDS - V.I. 169, 45.34/8.56 =5.30
Havoline Syn SN 5W-30, PQIA - V.I. 177, 53.5/10 =5.35
PP SN 0W-20, PDS - V.I. 164, 46.8/8.6 =5.44
PP SN 5W-30, PQIA - V.I. 171, 55.1/10.0 =5.51
PU Euro SN 0W-40, PDS V.I. 186 75.3/13.6 =5.53
Havoline Syn SN 5W-20, PQIA - V.I. 155, 47.5/8.44 =5.66
PYB SN 5W-20, PQIA - V.I. 155, 49.4/8.7 =5.68
Motul 300V 0W-40, VOA - V.I. 174, =5.86
GC 0W-30, PDS - V.I. 167, 72/12.21 =5.93
Castrol 0W-40, VOA - V.I. 165, 79.19/12.95 =6.11
PU SN 5W-40, PDS - V.I. 166, 80.7/13.2 =6.11
Shell T6 5W-40, PDS - V.I. 170, 87/14.2 =6.13
M1 SN 5W-50, PDS - V.I. 180, 108/17.5 =6.17
RL SN 5W-50, PDS - V.I. 186, 130/21 =6.19
Motorcraft 5W-50, PDS - V.I. 181, 108/17.5 =6.48
RL SN 10W-60, PDS - V.I. 187, 170/26 =6.54
PYB SN 10W-30, PDS - V.I. 135, 69.7/10.53 =6.62
Rotella T3 10W-30, PDS - V.I. 144, 80/12 =6.67
Mobil Delvac 1 5W-40, PDS - V.I. 151, 102/14.8 =6.89
Castrol TWS 10W-60, PDS - V.I. 174, 168/24 =7.00
Rotella 15W-40, PDS - V.I. 135, 120/15.5 =7.74
Widman Dino 20W-50, V.I. 121, 175/18.8 =9.30
Mobil Spectra Syn Elite 150 (base oil), PDS - V.I. 206, 1705/156 =10.93

If your favourite oil isn't in the above list it's easy enough to calculated it's KV40/KV100 ratio to determine it's REAL V.I. and see where it would slot-in in the above.

Light oils with low ASTM V.I.'s can have remarkably high real V.I.s while even high V.I. heavy oils don't have high real V.I.'s.
It is a basic characteristic of oil that the heavier it is the more it's viscosity will change with temperature.

Since 40 grade and heavier oils can't have high real V.I.'s it should give one pause to question whether they really need to run a 40 grade oil in the first place, and if they do to consider choosing a high ASTM V.I. oil such as M1 0W-40 which at least minimizes the fact that heavy oils are disproportionately heavy on start-up for the viscosity gains that are made at higher temp's.







Fun?

 

[Garak]

Originally Posted By: Shannow
"Better" isn't more, or less...it's "closer to the newtonian" for the KV150 and the HTHS.

Certainly, but if one is looking at HTHS more in isolation, or at least within the specifications for a vehicle, the lower HTHS could be categorized as "better" for fuel economy, for instance. If it's lower than specified, it might be "better" for wear protection to move up.

used_0il: We can see some pretty impressive pour points on oils lacking the 0w-XX rating. The old CI-4+ Royal Purple 15w-40 had a pour point around -45 C or colder, if I recall correctly.