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#4636128 - 01/15/18 07:44 PM Synthetic base oil viscosity index
ZraHamilton Offline


Registered: 01/15/18
Posts: 92
Loc: Tennessee, United States
Is it true that some synthetic base oils have such a high viscosity index naturally, that no viscosity index improvers are needed in the finished oil?

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#4636169 - 01/15/18 08:45 PM Re: Synthetic base oil viscosity index [Re: ZraHamilton]
Shannow Offline


Registered: 12/12/02
Posts: 39927
Loc: 'Stralia
some...
If there's a synthetic oil that has a Viscosity Index in the 130-140 range, then there's a good chance it's CLOSE to VII free.

If it's in that range and a monograde, e.g.
https://www.amsoil.com/lit/databulletins/g27.pdf

then it's all basestock no VII.

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#4636183 - 01/15/18 09:00 PM Re: Synthetic base oil viscosity index [Re: ZraHamilton]
aquariuscsm Offline


Registered: 12/30/06
Posts: 18183
Loc: Dallas,Tx USA
So is the higher the viscosity index,the better?
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#4636237 - 01/15/18 10:37 PM Re: Synthetic base oil viscosity index [Re: aquariuscsm]
OVERKILL Offline


Registered: 04/28/08
Posts: 36470
Loc: Ontario, Canada
Originally Posted By: aquariuscsm
So is the higher the viscosity index,the better?


Depends on how you define better. High when all propped up with polymer will make for a more gradual slope, but a moderate VI with little to no prop-up means less VII to shear. PAO also carries with it the advantage of not requiring PPD's to achieve its excellent cold temperature performance.

Mobil 1 EP 0w-20 isn't the highest VI oil in the land, but given its PAO base, it will have little polymer in it and its cold temperature performance is a natural result of the base oil(s). I'd rather that over some tarted-up Group III concoction laden with VII's and PPD with a "stratospheric" VI wink
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#4636240 - 01/15/18 10:46 PM Re: Synthetic base oil viscosity index [Re: aquariuscsm]
MolaKule Offline


Registered: 06/05/02
Posts: 19042
Loc: Iowegia - USA
Originally Posted By: aquariuscsm
So is the higher the viscosity index,the better?


Much depends on what you mean by, "better."

For most finished lubricants one cannot make that blanket statement. A Group II with a certain amount of VII can show a high VI. But will it have increased oxidation resistance and be able to deal with temperature extremes as do majority Group IV and V finished lubricants? Probably not.

The Amsoil ACD mentioned above is one of the few exceptions.

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#4636248 - 01/15/18 11:04 PM Re: Synthetic base oil viscosity index [Re: aquariuscsm]
Shannow Offline


Registered: 12/12/02
Posts: 39927
Loc: 'Stralia
Originally Posted By: aquariuscsm
So is the higher the viscosity index,the better?


The history of measuring and quoting the VI is based on the types of base oils that were available "back in the day".

Some fields showed a much smaller change in viscosity with temperature than others. The "best" were given an arbitrary number of 100, and the worst 0...then everything else compared to that scale.

With changes in refining, and synthetics, numbers above 100 were obtained.

So YES, higher VI in a basestock is a good thing, but VI is oft treated as the holy grail in spite of the problems that it brings (e.g. Molakule's post, and OVERKILL's jacked up on plastic example)...there have been bizarre statement made on the site that an oil sheared out of grade (reduced oil film thickness), but maintained it's viscosity index.

Old convo here

https://bobistheoilguy.com/forums/ubbthreads.php/topics/3022346/2

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#4636346 - 01/16/18 06:46 AM Re: Synthetic base oil viscosity index [Re: ZraHamilton]
aquariuscsm Offline


Registered: 12/30/06
Posts: 18183
Loc: Dallas,Tx USA
_________________________
1996 Nissan 300ZX 5-speed,Arctic Pearl(#175 of 300)
Quaker State Ultimate Durability 10W30
2012 Honda Accord Coupe EX-L 2.4,auto,San Marino Red
Pennzoil Platinum 0W20



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#4636384 - 01/16/18 07:40 AM Re: Synthetic base oil viscosity index [Re: aquariuscsm]
lukejo Offline


Registered: 09/21/11
Posts: 404
Loc: IL
So, is PUP 5w30 with a VI of 172, but supposedly just a Griup III+, just really propped up with polymers?
Yet, it's touted for severe applications, with a history of great UOA's with very minimal shearing.
(Not a rhetorical question...I really want to know where its high VII comes from...)

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#4636399 - 01/16/18 07:50 AM Re: Synthetic base oil viscosity index [Re: lukejo]
OVERKILL Offline


Registered: 04/28/08
Posts: 36470
Loc: Ontario, Canada
Originally Posted By: lukejo
So, is PUP 5w30 with a VI of 172, but supposedly just a Griup III+, just really propped up with polymers?
Yet, it's touted for severe applications, with a history of great UOA's with very minimal shearing.
(Not a rhetorical question...I really want to know where its high VII comes from...)


172 is not really that high, but yes, it would have VII's in it. Mobil 1 5w-30 has the same VI of 172 BTW.

Mobil 1 AFE 0w-30 has a VI of 166 and is partially PAO-based.
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#4636474 - 01/16/18 09:28 AM Re: Synthetic base oil viscosity index [Re: ZraHamilton]
Tom NJ Offline


Registered: 07/27/06
Posts: 2103
Loc: Virginia
While a high base oil VI may require less VI Improver, there is also oxidative stability to consider. In the hydrocarbon family, VI correlates well to oxidative stability since the less stable components tend to have lower VIs. By removing or restructuring these less stable components the VI increases. This is what hydrocracking achieves.

The most oxidatively stable components from crude oil derivatives are saturated linear hydrocarbons, but these waxy chemicals exhibit a freeze point upon cooling and are therefore undesirable and mostly removed. The next best for oxidative stability is saturated branched hydrocarbons as the branching eliminates the freeze point tendency, thus allowing a true pour point. PAOs are mixtures of saturated branched hydrocarbons and have the highest oxidative stability. Group III base oils are next as hydrocracking restructures the low VI less stable molecules, mostly into branched molecules.

The same correlation of VI to oxidative stability is not necessarily seen in other chemical families. For example, many vegetable based esters have very high VIs, up to 200+, yet are less stable than Group I hydrocarbons due to unsaturation. And the PAG family can also have very high VIs yet are less stable than POEs and diesters with lower VIs.

Keep in mind, however, that these differences in oxidative stability can be overwhelmed by a good anti-oxidant package, so it is once again the finished formulation that actually dictates the performance of the oil.

Tom NJ/VA

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#4636594 - 01/16/18 11:12 AM Re: Synthetic base oil viscosity index [Re: Tom NJ]
kschachn Offline


Registered: 12/26/05
Posts: 9420
Loc: Upper Midwest
Originally Posted By: Tom NJ
Keep in mind, however, that these differences in oxidative stability can be overwhelmed by a good anti-oxidant package, so it is once again the finished formulation that actually dictates the performance of the oil.

Once again.
_________________________
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1999 Toyota Sienna, 394K
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#4636700 - 01/16/18 01:03 PM Re: Synthetic base oil viscosity index [Re: Tom NJ]
PeterPolyol Offline


Registered: 03/06/16
Posts: 1345
Loc: toronto
Thank you Tom for another quality post!

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#4638849 - 01/18/18 01:48 PM Re: Synthetic base oil viscosity index [Re: ZraHamilton]
Linctex Offline


Registered: 12/31/16
Posts: 6178
Loc: Waco, TX
VERY informative, Tom NJ/VA!

Thank You!
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