Viscosity Index. When is the VI considered high.

[SR5]

Originally Posted By: Shannow
Early on, and knowing that high VI was "good", chemists started to find additives that are called "Viscosity Index Improvers".
.
.
.

Because of this behaviour, and the fact that these multigrade oils weren't offering the protection that their grade suggested, HTHS (High temperature, high shear...150C, and 10^6 shear rate, quite typical of a big end at a reasonable RPM) was included alongside the grade as a minimum. The minimum was (naturally) lower than was typical for a monograde no VII oil.

e.g.
SAE30, which would typically have an HTHS of 3.5, was given an HTHS minimum of 2.9.
SAE20, which would normally have an HTHS of 2.9, was given an HTHS minimum of 2.6.
SAE40, which would normally be 4.3+ HTHS was split 0W, 5W, and 10W 40 (passenger grades) were given a minimum of 2.9, and 15W, 20W, 25W, and SAE40 (heavy duty grades) given a 3.7 minimum.

The 40 grades were fixed in 2013, with 3.5 and 3.7 targets respectively

Thanks for the excellent tutorial Shannow

 

[shDK]

Originally Posted By: Shannow
Originally Posted By: shDK
But when is the VI considered high ? And exactly what does a good high VI tell about an oil?

Thanks all, and have a nice weekend.

Søren


As to what it tells you about an oil ?

https://bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=3022346

Not much really, as you don't know how the oil was built.

Was it a 140VI basestock with an amount of VII added to get it to 208 ?
Was it a 120VI basestock with a lot more VII added to get it to 208 ?

What VIIs were used, and how stable are they?

What was the oil designer's intent ?
e.g. did they intend shear to take place early (like some of the Japanese OEMs DID) so that economy was bolsted, still within the existing grade structure (that's before 16, 12, and 8 were introduced).

By comparing the Kinematic Viscosities of the oil with the high shear viscosities for that lubricant you can at least get a feel for how much the oil has been "modified" by the addition of these polymers.

For your Castrol 0W20, the ratio of HTHS to theoretical is 82%.
For my Castrol Edge 5W30 (A3/B4), the ratio of HTHS to theoretical is 94%, and VI is "only" 165.

Yours appears to have a relatively light basestock for it's grade, and more influence by VII polymers.


Being that the oil I used seems to be a light oil with high amount of VI improvers. Would you consider that as a bad, or maybe a less god 0w-20 oil compared to others? If it is bad. I might consider flushing it out.

 

[Shannow]

Originally Posted By: shDK
Being that the oil I used seems to be a light oil with high amount of VI improvers. Would you consider that as a bad, or maybe a less god 0w-20 oil compared to others? If it is bad. I might consider flushing it out.


It's not bad, and certainly doesn't warrant flushing, especially if that's the grade in your owner's manual.

I'm personally not a fan of uber high VI oils like that one, and make different choices.

The Japanese OEMs seem to agree with me in their pressure to have the 0W16 grade formalised, having lower VIs, and a lesser VII influence.

 

[shDK]

Originally Posted By: Shannow
Originally Posted By: shDK
Being that the oil I used seems to be a light oil with high amount of VI improvers. Would you consider that as a bad, or maybe a less god 0w-20 oil compared to others? If it is bad. I might consider flushing it out.


It's not bad, and certainly doesn't warrant flushing, especially if that's the grade in your owner's manual.

I'm personally not a fan of uber high VI oils like that one, and make different choices.

The Japanese OEMs seem to agree with me in their pressure to have the 0W16 grade formalised, having lower VIs, and a lesser VII influence.



My owners manual states 0w-20 as the best choice. 5w30 can be used. But then you should not try to start the car below -15 Celsius. It is a pretty new engine design, so I guess it is designed to run on 0w-20.

Would you then say that the Castrol I use is a good quality oil? Another reason I choose it. Was because it is what Suzuki in the UK advice to use that oil. Of course castrol is also British.

Thanks a lot for your good posts.

 

[OVERKILL]

Originally Posted By: shDK
Originally Posted By: Shannow
Originally Posted By: shDK
Being that the oil I used seems to be a light oil with high amount of VI improvers. Would you consider that as a bad, or maybe a less god 0w-20 oil compared to others? If it is bad. I might consider flushing it out.


It's not bad, and certainly doesn't warrant flushing, especially if that's the grade in your owner's manual.

I'm personally not a fan of uber high VI oils like that one, and make different choices.

The Japanese OEMs seem to agree with me in their pressure to have the 0W16 grade formalised, having lower VIs, and a lesser VII influence.



My owners manual states 0w-20 as the best choice. 5w30 can be used. But then you should not try to start the car below -15 Celsius. It is a pretty new engine design, so I guess it is designed to run on 0w-20.

Would you then say that the Castrol I use is a good quality oil? Another reason I choose it. Was because it is what Suzuki in the UK advice to use that oil. Of course castrol is also British.

Thanks a lot for your good posts.


That's a strange statement in the manual due to the fact that the 5w-xx designation has its performance metrics for pumpability and cranking set at -35/-30C respectively

 

[shDK]

Originally Posted By: OVERKILL
Originally Posted By: shDK
Originally Posted By: Shannow
Originally Posted By: shDK
Being that the oil I used seems to be a light oil with high amount of VI improvers. Would you consider that as a bad, or maybe a less god 0w-20 oil compared to others? If it is bad. I might consider flushing it out.


It's not bad, and certainly doesn't warrant flushing, especially if that's the grade in your owner's manual.

I'm personally not a fan of uber high VI oils like that one, and make different choices.

The Japanese OEMs seem to agree with me in their pressure to have the 0W16 grade formalised, having lower VIs, and a lesser VII influence.



My owners manual states 0w-20 as the best choice. 5w30 can be used. But then you should not try to start the car below -15 Celsius. It is a pretty new engine design, so I guess it is designed to run on 0w-20.

Would you then say that the Castrol I use is a good quality oil? Another reason I choose it. Was because it is what Suzuki in the UK advice to use that oil. Of course castrol is also British.

Thanks a lot for your good posts.


That's a strange statement in the manual due to the fact that the 5w-xx designation has its performance metrics for pumpability and cranking set at -35/-30C respectively

I see your point. That is however what it say.

 

[BrocLuno]

Originally Posted By: OVERKILL
Originally Posted By: ARCOgraphite
Bach donut No1 whac the startling VI of base oil mix?
You have but jus fini produit.

208 is, like, wicked toasted.

An, Son of Z@ren, thin for jus a momentum that, at the 17C you pour in wale coverlet = to 20W50 grade warm in hardly motorcycle. So maybe 37cSt for this produit?


Serious question: Are you having a stroke? You may want to seek medical attention immediately. I'm not trying to be a clown, if this was not written intentionally to be gibberish, you need to call 911, you may be having a medical emergency.


He's trying to do his his hill billy - bayou french thing. Try saying it with an accent

 

[OVERKILL]

Originally Posted By: BrocLuno
Originally Posted By: OVERKILL
Originally Posted By: ARCOgraphite
Bach donut No1 whac the startling VI of base oil mix?
You have but jus fini produit.

208 is, like, wicked toasted.

An, Son of Z@ren, thin for jus a momentum that, at the 17C you pour in wale coverlet = to 20W50 grade warm in hardly motorcycle. So maybe 37cSt for this produit?


Serious question: Are you having a stroke? You may want to seek medical attention immediately. I'm not trying to be a clown, if this was not written intentionally to be gibberish, you need to call 911, you may be having a medical emergency.


He's trying to do his his hill billy - bayou french thing. Try saying it with an accent

If that's the case I'm not sure if I am to be relieved or further put off, LOL!

 

[A_Harman]

Originally Posted By: shDK
For a while I have working on choosing the 0w-20 oil I wanted to use your in the family car. And last Sunday I poured a 0w-20 into an engine for the first time. It really is verry thin. I ended choosing Castrol magnatec pro gf 0w-20. I normally never choose castrol products. But choose it because it had the highest VI( 208 )

But when is the VI considered high ? And exactly what does a good high VI tell about an oil?

Thanks all, and have a nice weekend.

Søren


Shannow pretty much explained the meaning of VI and its advantages and disadvantages.
Not much to add there.

I did an overall calculation of VI's that the PQIA published for a large population of synthetic oils and got 165. Almost all multigrade synthetics for the mass market cluster in the 160-170 range these days. To really move the needle, I think an oil needs to have VI above 180 to be considered "high". But VI by itself is not the be-all and end-all of oil characteristics. A high VI will contribute to better fuel economy as long as it is goes with low HTHS, if specified by the manufacturer.

 

[fdcg27]

I too chased this false god until I came to the realization that VIs above 180 or so are really the product of high VII treat rates.
This also explains why high VI oils like TGMO 0W-20 can also offer only mediocre performance at the 0W end as opposed to the lower VI M1 0W-20, which blows TGMO away at the 0W end.
Better basestock blends tell in real cold.

 

[Shannow]

Yes,
back when I started this journey, I would always choose the widest grade spread that I could, working on the meme that wider spread (higher VI) was an automatically better oil.

These days my position has changed somewhat, in that I'll take a more (theoretically) shear stable oil with less VIIs, and maybe drop a high temp grade to boot.

Back in the day, 10W50 and 5W50 were my go to's
Now 5W30/10W30 in A3/B4 flavour.

 

[SR5]

Originally Posted By: Shannow
Yes,
back when I started this journey, I would always choose the widest grade spread that I could, ...

Back in the day, 10W50 and 5W50 were my go to's
Now 5W30/10W30 in A3/B4 flavour.


Same here mate, in the old days I was all over 10W-60 for it's large grade spread.

Now I'm 10W30 or 5W30 for my cars. If I want some heavy stuff I would be looking at grades like 15W-50.

I'm of the view that once your oil can start well on the coldest days you will see, then there is no point in getting a lower (colder start) winter grade oil. It just adds polymer VII's that you don't need. For VII's and PPD, As much as you need but not more than you need.

 

[zeng]

Originally Posted By: SR5
I'm of the view that once your oil can start well on the coldest days you will see, then there is no point in getting a lower (colder start) winter grade oil. It just adds polymer VII's that you don't need. For VII's and PPD, As much as you need but not more than you need.

Spot on , SR5.

 

[ARCOgraphite]

You cant figure out what I said?

We communicate this in my business so foreign hackers cant translate, though Cognoscenti should understand.

Did I guess the KV40?

The OP's very high Vi oil cold = 20w50 Warm
_______________________________

Anyone with over 500 post should know what a high VI oil is; and that >200 is extremely high.


I just watched the bizarre Son of Zorn on fox last week - so I folded that in.

peace out V

 

[ARCOgraphite]

Originally Posted By: shDK


I Think maybe the " son of zoren " is some kind of twisted mind offspring from my name. Which by the way doesn't mean " son of zoren " My first name Søren, means nothing and my last name, Hansen means " son of Hans "


No I was referencing a new TV show on FOX, "Son of Zorn" that mixes a Graphic novel "superhero" in animation and his "family" is in the flesh. Very bizarre and somewhat amusing.

 

[Jetronic]

Originally Posted By: Shannow
Yes,
back when I started this journey, I would always choose the widest grade spread that I could, working on the meme that wider spread (higher VI) was an automatically better oil.

These days my position has changed somewhat, in that I'll take a more (theoretically) shear stable oil with less VIIs, and maybe drop a high temp grade to boot.

Back in the day, 10W50 and 5W50 were my go to's
Now 5W30/10W30 in A3/B4 flavour.


Identical story here.

 

[DWC28]

If i could add a little more complication, consider the film thickness to be related to viscosity. The heavier the viscosity the thicker the film. How thick of a film do you need to stay in hydrodynamic regime? With better surface finishes you can get by with a lower viscosity.
VII are not made the same. Within a chemical type you will have different shear stability depending mostly on molecular weight. The molecular weight also effects thickening efficiency. The higher the mole weight the better the thickening and the worse the shear so things trade off. Liquid ball bearings have better shear than long chain OCPs. Also temperature is not the only property that effects viscosity as pressure and speed also contribute. Synthetics are thinner than mineral oils under high pressure. So if you want optimum film thickness you must consider; surface finish, load, temperature, speed, and VII molecular weight and shear stability. As a general rule the higher the VI, the more consistant the viscosity, but as someone here said, there is no free lunch.

 

[zeng]

Originally Posted By: DWC28
Also temperature is not the only property that effects viscosity as pressure and speed also contribute. Synthetics are thinner than mineral oils under high pressure. So if you want optimum film thickness you must consider; surface finish, load, temperature, speed, and VII molecular weight and shear stability.


+1

Btw, what's your take on the difference in percentage terms,of the pressure-viscosity coefficients between a Grp I/II mineral oil and that of a Grp III/III+ synthetics.
Is rule of thumb of 5% below that of Grp I/II at operating temp suffice?

 

[DWC28]

We tested three oils which we believe are representative of their class. A represents a PAO, B a mineral oil and C a naphthenic oil. The pressure-viscosity coefficient is measured either directly by assessing viscosity as a function of pressure using high-pressure apparatus, or indirectly by measuring film thickness in an optical interferometer. In the latter case, the pressure-viscosity coefficient is calculated from measured film thickness using an EHL film thickness equation. Although direct measurements may be more accurate, they are not readily available. AGMA 925-A03 gives pressure-viscosity coefficients derived from optical interferometry for many lubricants over a wide range of temperatures.
Oil A has 100C viscosity of 10cSt, 40C viscosity of 65 cSt, 150C viscosity of 4.2 cSt, viscosity index of 135, pressure viscosity coefficient (alpha) of 1.4 and viscosity @ 100C and 1GPa of 40.5.
Oil B has viscosity at 100C of 10 cSt, viscosity at 40C of 85, viscosity at 150C of 3.8, viscosity index of 97, PV of 1.8 and viscosity @ 1 GPa and 100C of 60.5
Oil C has viscosity at 100C of 10 cst, viscosity @ 40C of 105cSt, viscosity at 150 C of 3.6, viscosity index of 66 PV of 2.8 and viscosity @ 1GPa 100C of 165.5

If you are operating entirely in the hydrodynamic range the lowest viscosity will give you the lowest friction. So depending on conditions any of the three could be the best.

 

[zeng]

Originally Posted By: DWC28
A represents a PAO, B a mineral oil and C a naphthenic oil.
AGMA 925-A03 gives pressure-viscosity coefficients derived from optical interferometry for many lubricants over a wide range of temperatures.
Oil A has 100C viscosity of 10cSt, 40C viscosity of 65 cSt, 150C viscosity of 4.2 cSt, viscosity index of 135, pressure viscosity coefficient (alpha) of 1.4 and viscosity @ 100C and 1GPa of 40.5.
Oil B has viscosity at 100C of 10 cSt, viscosity at 40C of 85, viscosity at 150C of 3.8, viscosity index of 97, PV of 1.8 and viscosity @ 1 GPa and 100C of 60.5
Oil C has viscosity at 100C of 10 cst, viscosity @ 40C of 105cSt, viscosity at 150 C of 3.6, viscosity index of 66 PV of 2.8 and viscosity @ 1GPa 100C of 165.5

Thanks heaps,DWC28 .....
for the insightful numerical details on the elusive pv coef technicalities for deeper understanding of oils behaviours.

Am I right in guessing these are base oils properties?
Or Naphthenic C is Grp I VI 66 base oil with PV coef. 2.8;and
B is high end Grp I/ medium Grp II VI97 base oil with PV coef 1.8 ......
and thus would appreciate your valuable comments if Grp III/III+ would have a PV coef higher than that a PAO's 1.4 but below Grp II's 1.8 ?
Wish my question is not dumb