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Help a not-so-noob: shear stability theory. #5292178 12/12/19 08:03 AM
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OilStasher Offline OP
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Hi everyone. Been lurking for years. I already feel like I know most of you and know quite a bit about oil and the site. Feels good to finally make it official.

I have a question about shear stability. Please correct me anywhere if I'm wrong. To my understanding, the smaller the viscosity (number) spread between the winter rating and 'hot' (100°C) rating, the more shear stable the oil is. So in theory a 5W-20 should be far more stable than a 5W-50. Right?

That said, let's go off topic a bit and talk about the winter viscosity rating of oil. The 5 in 5W-20 is the winter rating. I'm fairly sure that the "5" at a very cold temperature is actually far more viscous than the "20" at 100°C, contrary to what most people think. Oil 'thins' as it gets hotter. I'm assuming I'm correct so far?

So now my real question:

If the first two statements are true individually, how is it possible that both are true at the same time?

I would think based on the above statements that a [theoretical] 0W-60 would be the most shear stable oil out there, and a 0W-16 would shear like crazy. 0W-60 would be 'thin' (which is still kinda thick) at freezing temperatures, but only thin a small amount to a 'thick' 60 at 100°C. A 0W-16 is still 0W in the cold (which once again I presume is kinda thick compared to the viscosity at 100°C). The change in viscosity over the temperature spread seems to be less with a 0W-60. It doesn't have to thin much at all. Whereas a 0W-16 has to go from a thicker viscosity when cold to a crazy thin 16 viscosity at 100°C.

Perhaps you all can clear this up for me? Thanks!

Last edited by OilStasher; 12/12/19 08:08 AM.

Sludge-Ushering, Problematic, Economically-Retarded, Toxic, Egregious, Certifiably Horrible. Just like the company that sells it. cool
Re: Help a not-so-noob: shear stability theory. [Re: OilStasher] #5292192 12/12/19 08:11 AM
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OVERKILL Offline
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Yeah, you are completely lost. Let me try and make this a bit clearer:

The Winter rating of an oil is simply the oil's ability to pass the CCS and MRV requirements at a given set of temperatures. It has no formal applicable viscosity figure associated with it, just a loose set of limits defined by the SAE. So whether it's a 0w-8 or a 0w-50, all that means is that it was able to pass CCS and MRV at -35C and -40C respectively.

ALL oils thicken as they cool. Some 0w-xx's may actually thicken MORE than their 5w-xx counterparts, but will not have the viscosity "wall" that occurs when the waxes in the base oil crystallize, driving up viscosity dramatically and causing it to fail meeting the CCS and MRV requirements for 0w-xx.

GENERALLY, the narrower the spread between the Winter rating and the 100C visc, the less VII polymer used in the oil. This is because you need a lighter base oil to meet the lower Winter ratings. This base oil is then "pumped up" with VII to meet the 100C target. HOWEVER, there are exceptions. A lubricant using a PAO base can get away with a heavier base blend and less VII than one using your run of the mill Group III or especially Group II. So if all things were equal (same base used) then the rule holds true, however that's often not the case. XOM for example uses significantly more PAO in many of their 0w-xx products, some being almost entirely PAO-based like their EP and AP 0w-20's, so in this case, these oils, despite the spread, may actually have LESS VII than some cheaper based 5w-20's.

Does that make sense?


2019 RAM 1500 Sport - Mobil 1 EP 0w-20, FRAM Ultra
2020 Grand Cherokee SRT - Ravenol SSL 0w-40, FRAM Ultra
Re: Help a not-so-noob: shear stability theory. [Re: OilStasher] #5292214 12/12/19 08:34 AM
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buster Offline
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^ what OVERKILL said.

Generally speaking, the narrower the spread the more shear stable, all things equal. However, take Mobil 1 EP 0w20 and 5w20. The 0w20 is predominately PAO based, which will have a naturally higher VI than the 5w20 EP which is using less PAO and more Visom. It's likely the 5w20 EP uses more VII's. Then you get into the quality and shear stability of the VII as there are many. As a general rule though, yes the less spread the more shear stable.


2019 Frontier Pro 4X - RGT 5w30
2019 Impreza Sport - OE fill
Re: Help a not-so-noob: shear stability theory. [Re: OilStasher] #5292231 12/12/19 09:02 AM
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krismoriah72 Offline
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If you really want to get confused... There is a guy on here running 15w40 in his Prius with success... and plenty of hard working trucks using 0w20 Rotella Gas Truck..

Re: Help a not-so-noob: shear stability theory. [Re: OilStasher] #5292239 12/12/19 09:10 AM
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Mad_Hatter Offline
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Originally Posted by OilStasher

Perhaps you all can clear this up for me? Thanks!

Just because a particular lube uses a viscosity modifier doesn't make it necessarily "bad". Not all viscosity modifiers (viscosity index improvers, interchangeably) are created equal. Viscosity modifiers have assigned to it a SSI, shear stability index. The higher the SSI the better. High quality VM's can actually repair themselves once they're no longer subjected to the shearing condition, as a result any shear thinning is temporary and not permanent.

There is no way that I know of, besides subjecting a lube to tests of it's shear stability, to ascertain the quality of the VM used. That's gonna be something only the formulator knows.

Re: Help a not-so-noob: shear stability theory. [Re: krismoriah72] #5292257 12/12/19 09:41 AM
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StarCaller Offline
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Originally Posted by krismoriah72
If you really want to get confused... There is a guy on here running 15w40 in his Prius with success... and plenty of hard working trucks using 0w20 Rotella Gas Truck..



I'm running 0w-40 in my prius since the second day I got it from the dealer /
no problem or use of oil at all after like 80.000 miles /

Re: Help a not-so-noob: shear stability theory. [Re: krismoriah72] #5292278 12/12/19 10:06 AM
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hallstevenson Offline
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Originally Posted by krismoriah72
If you really want to get confused... There is a guy on here running 15w40 in his Prius with success... and plenty of hard working trucks using 0w20 Rotella Gas Truck..

So what you're saying is, there's no need to overthink your choice in oil ? grin Put modern oil in your vehicle and the chances of it having an oil-related engine failure are pretty slim ?

Re: Help a not-so-noob: shear stability theory. [Re: OilStasher] #5292375 12/12/19 11:52 AM
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geeman789 Offline
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Originally Posted by OilStasher


That said, let's go off topic a bit and talk about the winter viscosity rating of oil. The 5 in 5W-20 is the winter rating. I'm fairly sure that the "5" at a very cold temperature is actually far more viscous than the "20" at 100°C, contrary to what most people think.



The first numbers, the 0W etc part, might be better thought of like a letter grade for severe winter use. It would certainly eliminate much of the confusion with the winter rating.

0w is excellent. A

5w is good. B

10w is average. C

15w is marginal. D

20w is below average. F


Saying that a given winter rated oil DOES NOT EXCEED certain max viscosity limits, in two specific tests, at two different temperatures, doesn't really make things clear ...





Last edited by geeman789; 12/12/19 11:53 AM.

2011 SUBARU Impreza 5-door manual / 2016 HONDA Pilot / 2011 MAZDA 2 auto
Re: Help a not-so-noob: shear stability theory. [Re: Mad_Hatter] #5292404 12/12/19 12:18 PM
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Originally Posted by Mad_Hatter
The higher the SSI the better.


Incorrect. The lower the SSI, the better. It refers to the percentage of viscosity loss with use. A really stout VM like polybutadiene or stronger OCPs would have an SSI of 24 (24% viscosity loss) while a weaker OCP, such as what makes up the bulk of Lucas Oil Stabilizer, would have a higher SSI around 50.


"He who is without oil, shall throw the first rod." - Compressions 9:1
Re: Help a not-so-noob: shear stability theory. [Re: RDY4WAR] #5292422 12/12/19 12:35 PM
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Originally Posted by RDY4WAR
Originally Posted by Mad_Hatter
The higher the SSI the better.


Incorrect. The lower the SSI, the better. It refers to the percentage of viscosity loss with use. A really stout VM like polybutadiene or stronger OCPs would have an SSI of 24 (24% viscosity loss) while a weaker OCP, such as what makes up the bulk of Lucas Oil Stabilizer, would have a higher SSI around 50.

Oop's..I had it backwards, my bad.. thanks for setting the record straight.👍 (TE is the value that's higher, the better right?)

Re: Help a not-so-noob: shear stability theory. [Re: RDY4WAR] #5292423 12/12/19 12:36 PM
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DrDanger Offline
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Originally Posted by RDY4WAR
Originally Posted by Mad_Hatter
The higher the SSI the better.


Incorrect. The lower the SSI, the better. It refers to the percentage of viscosity loss with use. A really stout VM like polybutadiene or stronger OCPs would have an SSI of 24 (24% viscosity loss) while a weaker OCP, such as what makes up the bulk of Lucas Oil Stabilizer, would have a higher SSI around 50.


Do you have a link to some general info on SSI of VM's? I (and many here I guess ) would very much appreciate that.

Re: Help a not-so-noob: shear stability theory. [Re: OilStasher] #5292452 12/12/19 01:02 PM
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benjy Offline
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as noted there are many UNKNOWN variables in todays lubricants that only the BLENDER or a pro like MOLA understands if given complete specs. on machinery lubrication there was a graph showing how much faster a group III + lower thickens in the cold as well as they thin more in the heat. remember cold aka winter specs are at 40C aka 104F from there all is downhill. real synthetic PAO + Ester oils are totally pure with NO wax present but lesser oils refined from CRUDE have some or some more depending on the group. average joe will NEVER know + understand all there is to know about lubricants!! looking at Redline Ester lubes shows that lighter blends have less durability than slightly thicker ones even thou base oils are some of the best!! everything today is made to a price point so don't expect the best from cheaper lubricants IMO, thou lubes have surely improved even for a mid priced fake synthetic!!

Re: Help a not-so-noob: shear stability theory. [Re: benjy] #5292466 12/12/19 01:13 PM
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kschachn Offline
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Originally Posted by benjy
as noted there are many UNKNOWN variables in todays lubricants that only the BLENDER or a pro like MOLA understands if given complete specs. on machinery lubrication there was a graph showing how much faster a group III + lower thickens in the cold as well as they thin more in the heat. remember cold aka winter specs are at 40C aka 104F from there all is downhill. real synthetic PAO + Ester oils are totally pure with NO wax present but lesser oils refined from CRUDE have some or some more depending on the group. average joe will NEVER know + understand all there is to know about lubricants!! looking at Redline Ester lubes shows that lighter blends have less durability than slightly thicker ones even thou base oils are some of the best!! everything today is made to a price point so don't expect the best from cheaper lubricants IMO, thou lubes have surely improved even for a mid priced fake synthetic!!

Lol, what?


1994 BMW 530i, 251K
1996 Honda Accord, 280K
1999 Toyota Sienna, 430K
2000 Toyota ECHO, 284K
Re: Help a not-so-noob: shear stability theory. [Re: benjy] #5292498 12/12/19 01:42 PM
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Originally Posted by benjy
as noted there are many UNKNOWN variables in todays lubricants that only the BLENDER or a pro like MOLA understands if given complete specs. on machinery lubrication there was a graph showing how much faster a group III + lower thickens in the cold as well as they thin more in the heat. remember cold aka winter specs are at 40C aka 104F from there all is downhill. real synthetic PAO + Ester oils are totally pure with NO wax present but lesser oils refined from CRUDE have some or some more depending on the group. average joe will NEVER know + understand all there is to know about lubricants!! looking at Redline Ester lubes shows that lighter blends have less durability than slightly thicker ones even thou base oils are some of the best!! everything today is made to a price point so don't expect the best from cheaper lubricants IMO, thou lubes have surely improved even for a mid priced fake synthetic!!


Your posts are getting more and more outrageous over the last few months

Re: Help a not-so-noob: shear stability theory. [Re: benjy] #5292515 12/12/19 01:57 PM
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RDY4WAR Offline
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Originally Posted by benjy
as noted there are many UNKNOWN variables in todays lubricants that only the BLENDER or a pro like MOLA understands if given complete specs. on machinery lubrication there was a graph showing how much faster a group III + lower thickens in the cold as well as they thin more in the heat. remember cold aka winter specs are at 40C aka 104F from there all is downhill. real synthetic PAO + Ester oils are totally pure with NO wax present but lesser oils refined from CRUDE have some or some more depending on the group. average joe will NEVER know + understand all there is to know about lubricants!! looking at Redline Ester lubes shows that lighter blends have less durability than slightly thicker ones even thou base oils are some of the best!! everything today is made to a price point so don't expect the best from cheaper lubricants IMO, thou lubes have surely improved even for a mid priced fake synthetic!!


There's so much wrong with this post I don't know where to begin.

1) PAO oils are made from crude. Esters are made from reacting alcohols with acids.
2) Esters have very poor cold temperature performance and a VI usually in the 70-90 range. They are used in PAO oils for solubility of the add pack and that's about it. Higher amounts of ester add more solubility which is great for cleaning out a sludged up engine. (see: Valvoline Premium Blue Restore) It's not great for the commoner. A racing application that needs stability at 300+*F, sure.
3) For 95% of the cars on the road, they'd never notice the difference between a group III and IV base oil as they don't operate in the extremes where that would make a difference. Minor things like a lower NOACK and lower hydrodynamic friction from PAO oils can be beneficial at any temperature, but usually aren't worth the investment.
4) Where are you seeing Red Line "lighter" lubes being less durable?


"He who is without oil, shall throw the first rod." - Compressions 9:1
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