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Uniform molecule size and viscosity modifiers #5215678 09/17/19 10:46 PM
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Rav4H2019 Offline OP
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When viscosity modifiers are added to a synthetic base oil, say in m1 0w20 ep or 0w40, then at operating temperature are all the molecules of same size ? Uniform molecule size is touted in selling synthetic oils. Are the molecules from the viscosity modifier larger than those of base oils?

Last edited by Rav4H2019; 09/17/19 11:00 PM.
Re: Uniform molecule size and viscosity modifiers [Re: Rav4H2019] #5215734 09/18/19 03:17 AM
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The whole molecule size thing ( from what i've been able to gather ) is more of a marketing gimmick than anything.


1975 Ford Capri II Ghia 3000 V6 - 315k, Repsol Elite Super 20W-50
1988 Ford Escort XR3i Cabrio - 110k, Valvoline Maxlife 10W-40

Re: Uniform molecule size and viscosity modifiers [Re: Rav4H2019] #5215813 09/18/19 07:14 AM
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We need the data from a Chemist who works for an oil company to answer that. Ed


2014 CX5 Touring 2.5L :-)
Re: Uniform molecule size and viscosity modifiers [Re: Rav4H2019] #5215815 09/18/19 07:17 AM
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Not all the same size but probably the distribution curve of molecular weight/size is much narrower for a PAO or a GTL oil than one that is refined from dino drippings.


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Re: Uniform molecule size and viscosity modifiers [Re: Rav4H2019] #5215888 09/18/19 08:35 AM
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Originally Posted by Rav4H2019
When viscosity modifiers are added to a synthetic base oil, say in m1 0w20 ep or 0w40, then at operating temperature are all the molecules of same size ? Uniform molecule size is touted in selling synthetic oils. Are the molecules from the viscosity modifier larger than those of base oils?

What the heck, I'll take a stab at this. I don't think they are all exactly uniform in size, otherwise you wouldn't have permanent shear loss. So some of the uncoiled VM polymers get chopped up, reducing the VM's ability to resist the flow of the base oils molecules.

Now there are really high quality VM's that better resist this shearing. You see these used in extended drain lubes for example.

( I've read that higher molecular weight VM polymers do a great job of thickening the oil but are more prone to shear (larger size??) and the treat rates are lower when using these high molecular weight VM's. Conversely, low molecular weight polymers are better at resisting shear but not so much at thickening hence the treat rate (quantity needed) is higher)

Last edited by Mad_Hatter; 09/18/19 08:36 AM.
Re: Uniform molecule size and viscosity modifiers [Re: Rav4H2019] #5216010 09/18/19 10:31 AM
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It’s a bunch of marketing baloney.

Think about it logically. Molecular size is measured In Angstroms.

1 angstrom = 1/10,000 Microns

1/1000 of an inch or mil is used in engine measurement = 25 Microns

An oil molecule = ~30 Angstroms

The argument that synthetic oils molecular size being more uniform than conventional is completely irrelevant in a fully formulated motor oil when only ~80% is base. VM’s are significantly larger - not to mention some of the other hodgepodge of ingredients that may be too.


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Re: Uniform molecule size and viscosity modifiers [Re: Rav4H2019] #5216014 09/18/19 10:41 AM
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So when synthetic oil with VM''s is being squeezed in between two metal plates, VM''s are providing the padding at operating temperature they are larger ?

Last edited by Rav4H2019; 09/18/19 10:57 AM.
Re: Uniform molecule size and viscosity modifiers [Re: Rav4H2019] #5216021 09/18/19 10:53 AM
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This goes back to the 70's when I started using synthetic oil; At that time it was stated that dyno oil has 3 types of molecules small-medium & large.

The small & large molecules get burnt off and end up as deposit on your valves and piston head while the medium size ones lubricate.

I'm pretty sure that may not be possible to make all the molecules, no matter the category, uniform in size so there must be an amount of give & take.

Last edited by Pelican; 09/18/19 10:56 AM.
Re: Uniform molecule size and viscosity modifiers [Re: Rav4H2019] #5216055 09/18/19 11:23 AM
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Originally Posted by Rav4H2019
So when synthetic oil with VM''s is being squeezed in between two metal plates, VM''s are providing the padding at operating temperature they are larger ?


So when synthetic oil with VM''s is being squeezed in between two metal plates, VM''s are providing the padding at operating temperature SINCE they are larger ?

Re: Uniform molecule size and viscosity modifiers [Re: Rav4H2019] #5216067 09/18/19 11:31 AM
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Originally Posted by Rav4H2019
So when synthetic oil with VM''s is being squeezed in between two metal plates, VM''s are providing the padding at operating temperature they are larger ?


Now we’re getting into pocket protector territory (not meant in the pejorative) of temporary polymer shear. What I understand is this phenomenon always occurs when the oil is squeezed enough between two surfaces for the VM polymers to align themselves like nesting spoons. To what degree of VM type and the base oil viscosity comes into play is the 64 thousand dollar question best answered by more learned members.

For further edification research traction coefficient and pressure viscosity constant on this topic. Very interesting reading.


Last edited by ndfergy; 09/18/19 11:36 AM. Reason: grammar

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Re: Uniform molecule size and viscosity modifiers [Re: Pelican] #5216069 09/18/19 11:33 AM
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Originally Posted by Pelican
This goes back to the 70's when I started using synthetic oil; At that time it was stated that dyno oil has 3 types of molecules small-medium & large.

The small & large molecules get burnt off and end up as deposit on your valves and piston head while the medium size ones lubricate.

I'm pretty sure that may not be possible to make all the molecules, no matter the category, uniform in size so there must be an amount of give & take.


So the smaller ones burn off as they are more prone to burn off. ? And the larger ones are carrying the load so to speak and hence burn off ?

Re: Uniform molecule size and viscosity modifiers [Re: Rav4H2019] #5216073 09/18/19 11:36 AM
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'14 Dodge Grand Caravan 3.6 Valvoline 5W20 Semi Synthetic
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Re: Uniform molecule size and viscosity modifiers [Re: ndfergy] #5216086 09/18/19 11:48 AM
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Originally Posted by ndfergy

The argument that synthetic oils molecular size being more uniform than conventional is completely irrelevant in a fully formulated motor oil when only ~80% is base. VM’s are significantly larger - not to mention some of the other hodgepodge of ingredients that may be too.

Really?

Setting fully synthetics PAO aside, Grp3 synthetics are hydrocracked.. the breaking of long change hydrocarbons into smaller uniform molecules. The resulting (designer) base oil has superior (to mineral) oxidative and thermal stability, higher VI and the highly processed (cracked) oil has a lower "traction coefficient" (lubricant friction) then grp2 mineral oils because of molecular uniformity.

Some Grp3 base stocks like Shell's GTL rival PAO in performance and some highly processed Grp2+ oils have viscosity indexes approaching Grp3. Chevron for example has a grp2+ with a VI of 118(119??) with a volatility of a grp3.

Synthetics v. Mineral

Last edited by Mad_Hatter; 09/18/19 11:51 AM.
Re: Uniform molecule size and viscosity modifiers [Re: FordCapriDriver] #5216096 09/18/19 12:00 PM
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Originally Posted by FordCapriDriver
The whole molecule size thing ( from what i've been able to gather ) is more of a marketing gimmick than anything.


Ditto.


"He who is without oil, shall throw the first rod." - Compressions 9:1
Re: Uniform molecule size and viscosity modifiers [Re: Rav4H2019] #5216101 09/18/19 12:06 PM
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I vote Ravenol for the best marketing program. /tongue in cheek

Even if their PDFs like the one linked are pure marketing hooey, it means something to me when a company will spend the time to tell you about its products in greater depth than competitors do. I've used the Ravenol DXG, and it seemed like a good oil other than I got d1G1 oil in a jug labeled d1G2; but since my vehicles don't require either cert, I use it anyway.

I'll be putting it in my Impreza before it snows, replacing some Amsoil SS 10W30.


De omnibus dubitandum.
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