Do ALL engines shear oil?

[oil_film_movies]

Originally Posted By: Speak2Mountain
My DI 2.5 V6 from Toyota sheared PP 5w30 to 20 in 3100 miles, according to Blackstone Labs.
Blackstone also reported: 98% of add pack still left and could prolly go to 5K easily.

How does Blackstone make a statement of % add pack remaining? I've never seen them account for additives that disappear out the tailpipe. Typically additive compounds based on moly, boron, zinc, etc. maintains their concentrations no matter how low the TBN gets. ... Seems weird.

Back to the actual subject, permanent VII shear (broken molecules), I have a crazy theory: New engines, with more sharp surface asperities and iron particles under 10 microns in size running around, shear oil more. I think I've observed UOA's with new engines having more shear. Also turbo'ed engines are rougher on oil and show more shear. Maybe my observations of new vs. broken-in engines are off, but its consistent with the way VII's die: more stress.

 

[Solarent]

I'd agree on Turbo engines, but I'm not sure about new vs old. That seems a strange to me and probably wouldn't have an impact

 

[kschachn]

Originally Posted By: oil_film_movies
Back to the actual subject, permanent VII shear (broken molecules), I have a crazy theory: New engines, with more sharp surface asperities and iron particles under 10 microns in size running around, shear oil more. I think I've observed UOA's with new engines having more shear. Also turbo'ed engines are rougher on oil and show more shear. Maybe my observations of new vs. broken-in engines are off, but its consistent with the way VII's die: more stress.

How would you know if a viscosity decrease was due to actual mechanical shearing or from fuel dilution? Do you trust the Blackstone numbers we most often see on here? New cars could possibly have worse fuel dilution as well.

 

[DeepFriar]

Originally Posted By: bigj_16
I think for general use on this board. most people understand that "shear" stands in for permanent viscosity loss. Temporary viscosity loss in this usage is not the issue, although they can be related, in some circumstances.
Her is an Oronite piece on this:
https://www.oronite.com/paratone/shearloss.aspx


+1. This has been my general understanding on BITOG. Do we need a better way of expressing the phenomenon in everyday use on the board?

I believe the claims of some synthetics about not needing "as much" polymer additives has to do with their "natural" viscosity indexes being so high. Not sure if anybody actually claims to have none although the esters probably come closest in practice. It was my understanding that straight weight oil does not "shear down" in use. Is that correct?

Some modern engines that use straight weight are marine but that appears to be changing.

 

[demarpaint]

Originally Posted By: bigj_16
Originally Posted By: demarpaint
Originally Posted By: Solarent
Originally Posted By: demarpaint
No, not in my case I have two UOA's for the same vehicle were both times the oil moved up a grade.One case was in 5K miles, the other in 6K miles. It did well in the application both times but "thickened." So saying All engines shear oil would be incorrect. There are other examples of oil "thickening" scattered about the UOA section.


You should go back and read my post. Just because you have an oil thickening over the life of the fluid doesn't mean that the engine doesn't shear the oil. It just means you have factors that also thicken the oil at work in your engine as well.


I wasn't referring to you, just making a point. There is a misconception which you alluded to. Many people seem to think oil shears to a "thinner" grade, and that always happens. Thickening is sometimes referred to as oxidation, where oil goes in the other direction. Bottom line oil can go up or down a grade, or more.


But what you have is thinned, oxidized oil going up a grade. Obviously, this is not a good thing. When I lived a long time ago, in a far, far galaxy, this is something I would see occasionally in testing. Usually it was from diluted, oxidized oil. So, what you have is fuel and pentane insolubles meeting or exceeding a viscosity, not oil(broadly speaking). But is that what you really want running around in your engine?

Diluting from what? Fuel in the oil according to both reports was just about non-existent as per testing and interpretation by people a lot more knowledgeable than I. No coolant or water in it either. The engine did quite well and the oil could have gone a bit longer than I ran it.

 

[demarpaint]

Originally Posted By: bigj_16
But is that what you really want running around in your engine?

It was a bit too late to edit:

Isn't that the whole premise behind changing your oil? A UOA report? And not trying to stretch every possible mile out of an OCI?

The people who read the report for this vehicle said everything was OK, and I landed on a 6K OCI going forward.

 

[oil_film_movies]

Originally Posted By: Solarent
I'd agree on Turbo engines, but I'm not sure about new vs old. That seems a strange to me and probably wouldn't have an impact

Somebody with better knowledge of micro-mechanics would know. "Molecular Mechanics", as in what happens during Brownian motion (where the molecules are in constant irregular motion with a velocity proportional to the square root of the temperature) in the presence of pressure and physical stress. My supposition is that hard metal iron and copper particles in the oil (under 10 microns or so) get cozy with the VII high aspect ratio shaped molecules when in boundary lubrication with a new engine's high asperities, causing the VII to break apart. Heat and pressure alone is tough on VII, as in the turbo example, especially some turbo bearings that get more hot than others. Of course rings see a ton of heat too, not just turbo bearings.

Sure those Blackstone fuel dilution estimates are based on flashpoint drops, yet when the flashpoint hasn't dropped much, it is hard to imagine there could be much fuel in there reducing kv100 viscosity. That leaves VII permanent mechanical shearing as the cause.

 

[Nick1994]

My GDI Sonata doesn't shear oil. UOA came back great.

 

[Solarent]

Originally Posted By: DeepFriar
Not sure if anybody actually claims to have none although the esters probably come closest in practice


What is your basis for the claim that "esters probably come closest" to having no VM in the formula? I've seen people make this claim before and I wonder where it came from.
Despite what you may think Group V oils are not higher performance than Group IV or even Group III. Group V oils is for everything that doesn't fit in Group I-IV, regardless of performance.