Do ALL engines shear oil?

Status
Not open for further replies.
Joined
Apr 7, 2017
Messages
553
Location
Mississippi
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

Sidenote: got the UOA done @ 3100 miles b/c I swear I smelled gasoline in the oil. Blackstone poo-poo that one too.

PP is a strong oil
 
Last edited:
Some engines are just better at it than others. The Nissan QR25DE is also known for shearing.

But we've all seen really long runs where the oil stays in the viscosity range. Driving conditions also play a role.
 
The 4GR-FSE is only direct injected. So the issues of oil dilution apply here. If the oil is thin and you smell fuel in it, what did blackstone say your fuel % was?
 
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

Sidenote: got the UOA done @ 3100 miles b/c I swear I smelled gasoline in the oil. Blackstone poo-poo that one too.

PP is a strong oil
Can you post the UOA? Usually Blackstone will put "TR" or "<.5%" or the actual level. If it is "<.05", you can probably smell it, and it is still dilution. Your oil probably diluted and sheared.
 
In a direct answer to your question. Yes all engines shear oil.

It is a common misunderstanding on this board and other places what is meant when we talk about oil shearing. Most people think of cutting up molecules and making the oil thinner. That is not what is meant. This is why we tried to address this in the revisions to the Motor Oil University section on the main page (see section 103)

In physics, "Shear forces" are what happens when two surfaces move past one another. When those surfaces are separated by a liquid (like engine oil) it is said that the oil is “shearing” - this does not mean the oil is breaking down or being cut up, it means that the viscosity is changing to allow more flow when the shear forces are high. When the two surfaces move past one another the directional shear force increases or decreases based on the fluid viscosity, temperature, load and speed. Incidentally these same factors are used when discussing the coefficient of friction described by tribologists as explained by the Stribeck curve.

Because all engines have moving parts, they all have shear forces that act on the oil. This is a good thing.

To understand the impact of shearing on engine oil, think about these 2 examples:
Ketchup - When you turn the bottle upside down, the ketchup doesn’t like to move. In order for it to flow, you give it a shake and apply some shear forces to it. The ketchup then “shears down” to a level which allows it to flow out of the bottle. Your engine oil also works the same way, when high shear forces are applied your engine oil also thins out. This is an example of a shear thinning fluid.

Cornstarch in water - With this mixture, when you increase the shear force (for example by hitting it with a mallet) the fluid thickens and becomes solid. It then thins out again when the shear forces are taken away. This is an example of a shear thinning fluid.

In engine oil, there are examples of when you would want an oil to either be thinner or thicker under load (or under a shear force) than when it is at rest. When passing through tight spaces or heavily loaded bearings (like on a cam shaft) if the oil is too thin, it won't keep the metal parts separated, if it is too thick, then energy efficiency is lost and you could end up with hot spots because the oil is not able to transfer heat away properly until it thins out more.

Viscosity modifiers are used to alter the way the lubricant flows under various shearing conditions. In high shear environments the oil may behave in one way, while in low shear environments it will behave a different way. The same is true under various temperature conditions. High temperature and high shear conditions are among the most severe from a viscosity perspective, which is why engine oil grades have a minimum HTHS viscosity set. Lower HTHS can produce fuel economy gains but must be balanced with additional performance to provide the same level of protection. Fortunately there are chemical engineers who specialize in Rheology who assist formulators in solving these complex issues.

In service most engine oils will temporarily "shear down" or reduce their viscosity when put under shear pressure and then return to their original viscosity when the oil moves to a different part of the engine where the shear forces are lower. This is a desirable trait as it allows the oil to maintain the proper viscosity under a wide variety of conditions that occur in the engine.

---

Coming back to your UOA testing. Your oil has lost viscosity and fallen out of grade. There are several reasons that could cause this: perhaps the oil has become diluted with a thinner material (ie fuel dilution), or perhaps the viscosity modifiers have changed in service - the molecules (polymer chains) may have been put under so much shear force that parts of the chain has become un-linked. This makes the molecules smaller and reduces their "thickening power" on the base oil mixture they are being used with - sometimes this is called permanent shear or shearing out of grade. Those are the two most common causes of permanent viscosity loss in service.

If left too long, oil can actually thicken as well. Thickening of the oil (an increase in viscosity) can result from the lighter fractions of the oil “evaporating” or “volatizing” at high temperatures. Most base oils are mixtures of both low viscosity and higher viscosity oils. It is the lower viscosity oils that have a tendency to evaporate and leave behind the higher viscosity oils with oxidation by-products, thus causing thickening of the engine oil over time.

Sorry for the long response, but I hope it helps you understand that shearing a good thing. For more information - go and read Motor Oil University, the revised version is much more informative and had the input of some really smart people from BITOG.
 
Last edited:
Actually oil never shears, correct? I don't see how you could break apart relatively short hydrocarbon molecules. I would think the short answer is that no engine shears oil but it may affect the viscosity modifiers. An oil without modifiers will not exhibit viscosity loss due to mechanical shear.

And to make it worse, nearly all the oil analysis we see on here (especially from Blackstone) have shown that they are unreliable at distinguishing between fuel dilution and actual shearing of viscosity modifiers. Even their ability to measure viscosity seems suspect.
 
Originally Posted By: kschachn
Actually oil never shears, correct? I don't see how you could break apart relatively short hydrocarbon molecules. I would think the short answer is that no engine shears oil but it may affect the viscosity modifiers. An oil without modifiers will not exhibit viscosity loss due to mechanical shear.


Who is using a monograde oil in the modern engine? I don't know anyone that does. OEM's certainly never recommend them. Far and away people are using multi-grade oils and that means they are using viscosity modifiers. I have yet to see a multigrade engine oil formula that doesn't contain them.
 
Originally Posted By: Solarent
Who is using a monograde oil in the modern engine? I don't know anyone that does. OEM's certainly never recommend them. Far and away people are using multi-grade oils and that means they are using viscosity modifiers. I have yet to see a multigrade engine oil formula that doesn't contain them.

No clue, and I wasn't advocating that anyone do so. I certainly don't. But the question was "Do ALL engines shear oil?" and my response was specific to that question, noting that it isn't the oil that is shearing.

Are all viscosity modifiers equally prone to mechanical shearing or are some better or worse than others? Does this translate into one fully-formulated oil having better or worse viscosity stability due to mechanical shear? Does the presence of fuel affect the stability of viscosity modifiers?

Do Reline and Amsoil 10W-30 contain viscosity modifiers?
 
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 did smell gas in the oil. Those of us with fuel dilution can smell gas on the dip stick. I think we need to think about extracting the oil fill when it seems to lose viscosity so the engine maintains the spec'd viscosity.
 
Are all viscosity modifiers equally prone to mechanical shearing or are some better or worse than others?
No depending on the molecular weight, type and shape of the molecule, they will have various properties including shear stability. The most common VM for passenger car engine oil is OCP based, and it is typically 25 SSI (shear-stability index) or 35 SSI. European formulas and high performance fuel economy oils often use a different kind of VM (not OCP).

Does this translate into one fully-formulated oil having better or worse viscosity stability due to mechanical shear?
Yes it does.

Does the presence of fuel affect the stability of viscosity modifiers?
Not from mechanical shearing of the polymer chains, but it can impact the overall viscosity performance of the fully-formulated oil

Do Reline and Amsoil 10W-30 contain viscosity modifiers?
I don't know but I expect they do. It is theoretically possible to formulate a 10W30 oil with 100% PAO and no VM. I've never seen one actually put into production though. That would be a question for their formulators. Personally I would prefer a higher performing oil that has VM's for the desirable traits I indicated in my first post, especially when OEM's are going thinner and higher performance across the board.
 
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.
 
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, it can often stay in grade. 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. A lot of factors come into play.
 
Last edited:
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?
smile.gif
 
Last edited:
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, it can often stay in grade. 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. A lot of factors come into play.


Doug has said that it is better for an oil to shear a bit than to oxidize.
 
Status
Not open for further replies.
Back
Top