Shearing: 5w30 dyno vs 10w30 dyno?

[akela]

Hi,
I am trying to get better understanding how VII work, and what shearing does to the oil. What's the advantage of 10w dyno against 5w dyno.

Looking at UOA for dyno oils, I can see that 10w30 is holding up the viscosity much better. After few kmiles, 10w30 is (more often than not) still in w30 area (around 10cSt). And 5w30 often shears down to something like 7.5-9 cSt, becoming 5w20.

Seen this table several times on different web pages (for example here):

SAE.............Kinematic
Viscosity.......(cSt)
................100° C Min
0W..............3.8
5W..............3.8
10W.............4.1
15W.............5.6
20W.............5.6
25W.............9.3

Let's imagine that we have removed all VII from 5w30 and 10w30 (both dino) oils. In another words, it sheared down completely to the "straight 5" and "straight 10". What will be the viscosity at the operating temperature in both cases? According to this table, it will be almost identical: 3.8 or 4.1 cSt. Is anything wrong with this data? If so, what would be the correct numbers?
(I'm quite new to BITOG, so if I am asking something obvious, please point me to the right direction...)

 

[gfh77665]

10-30 is a better oil for the US southland. I know, I know, the enlightened will scoff, but there is no doubt in our subtropical climes, 10-30 is an excellent choice, and 5-30 offers little or no advantages here. Agreed, in Canada and the north US, its a different story.

 

[tinmanSC]

You have answered your own question, if you look closely. In the case of conventional oil, it would shear down to an SAE 10 for 10W-XX, and an SAE 5 grade for 5W-XX. These are the viscosities at normal operating temperature (212 Deg. Fahrenheit). These are much too thin for the average engine. But you don't want to compare an SAE 5 to a 10 at operational temps, you want to compare an SAE 5 to an SAE 30. Bigger difference there. Remember, for practical purposes, shear in an engine is minimal in most cases. A 5W-30 MIGHT shear down to a 20, but unless you have been "abusing" the oil, that's as far as it will get.

If you want to compare 5W VS 10W, you gotta look at cold numbers.
http://www.bobistheoilguy.com/visc.html

 

[Tempest]

I don't think I've ever seen a 30 grade shear down to anything close to 7.5 cSt. Most shear down to low 9's with the occasional high 8, mostly because of fuel dilution.

VII's don't deal as well with pressure as does pure oil. That's why they don't protect as well, but there is more to it than that as AW additives come into play as well.

And these oils are not 5 or 10 grade oils with just VII added to them. They are blends of oils that when combined with the VII give the viscosity results desired.

 

[Colt45ws]

That table is talking about low shear rate minimum viscosity to get that 5W or 10W rating.
What matters is the 30 grade rating on the end after the W.
30 grade low shear rate viscosity is in the range 9.3-12.5cSt. High shear minimum viscosity is 2.9cP at 150C
So...
In order to be a 10W30 the low shear rate viscosity has to be in the range 9.3-12.5cSt@100C
In order to be a 5W30 the low shear rate viscosity has to be in the range 9.3-12.5cSt@100C
They have to be the same viscosity range at temp...
The 2.9 high shear rate viscosity will pretty much be what most 5W30 and 10W30s will spec out as, since it effects fuel economy and they have to get that API "Energy Conserving" donut.
If we are talking about off the shelf "Energy Conserving" oils, the differences between these two is so negligible as to be almost nonexistent except at extremely cold temps.

 

[orlzx6r]

Originally Posted By: tinmanSC
You have answered your own question, if you look closely. In the case of conventional oil, it would shear down to an SAE 10 for 10W-XX, and an SAE 5 grade for 5W-XX. These are the viscosities at normal operating temperature (212 Deg. Fahrenheit). These are much too thin for the average engine. But you don't want to compare an SAE 5 to a 10 at operational temps, you want to compare an SAE 5 to an SAE 30. Bigger difference there. Remember, for practical purposes, shear in an engine is minimal in most cases. A 5W-30 MIGHT shear down to a 20, but unless you have been "abusing" the oil, that's as far as it will get.

If you want to compare 5W VS 10W, you gotta look at cold numbers.
http://www.bobistheoilguy.com/visc.html



There is some bad information with this. A 5W-* or 10W-* does not start with a 5 or 10 weight oil. The first number is cold pumpability rating (the W stands for winter not weight).


Oil formulators can use multiple basestocks plus VII to create the desired oil. IF they left out the VII it's hard to say what SAE weight you would have.

 

[Spyder7]

My take is that a 10W30 should be slightly more sheer resistant due to needing less viscosity improvers. Synthetic of either grade should be more sheer resistant still because of better base stocks requiring less viscosity improvers again. Net result is that a 10W30 syn should be the best equipped to maintain its viscosity rating.

That said, cSt@100C provides a pretty broad range for the API spec. So it stands to reason that an oil that is thicker there should stay in grade longer. You could also go with a thin 5W40 which should only sheer down to a 30 weight, if avoiding oil sheering to a 20 weight is the goal.

To get some indication of how resistant the oil is, consider its total package: cSt@100, NOACK, and HTHS. Low NOACK and higher HTHS will indicate better base stocks, and or fewer viscosity improvers, which add up to it being better able to resist thinning.

Or the short answer: there is no simple answer.

-Spyder

 

[Gary Allan]

Quote:
There is some bad information with this. A 5W-* or 10W-* does not start with a 5 or 10 weight oil. The first number is cold pumpability rating (the W stands for winter not weight).



It wasn't always bad. That's how you could make a 10w-30. You took 5.35-
A 20w-20 may or may not have PPD added to meet the cold "w" spec.

 

[mechtech2]

I'd be more concerned with this if the engine had a timing chain.
They can chew up oil more.
I don't think that shear is a real problem for most street cars, except on paper.

 

[tinmanSC]

Originally Posted By: orlzx6r
Originally Posted By: tinmanSC
You have answered your own question, if you look closely. In the case of conventional oil, it would shear down to an SAE 10 for 10W-XX, and an SAE 5 grade for 5W-XX. These are the viscosities at normal operating temperature (212 Deg. Fahrenheit). These are much too thin for the average engine. But you don't want to compare an SAE 5 to a 10 at operational temps, you want to compare an SAE 5 to an SAE 30. Bigger difference there. Remember, for practical purposes, shear in an engine is minimal in most cases. A 5W-30 MIGHT shear down to a 20, but unless you have been "abusing" the oil, that's as far as it will get.

If you want to compare 5W VS 10W, you gotta look at cold numbers.
http://www.bobistheoilguy.com/visc.html



There is some bad information with this. A 5W-* or 10W-* does not start with a 5 or 10 weight oil. The first number is cold pumpability rating (the W stands for winter not weight).


Oil formulators can use multiple basestocks plus VII to create the desired oil. IF they left out the VII it's hard to say what SAE weight you would have.


Yes, this is true. The information was not to-the-letter always 100% totally accurate. I figured it was close enough for this general discussion. But you got me, thanks for crossing my t's and dotting my i's. =)

Edit: The Motor oil 101 on the main BITOG page talks about this. IMO, the language used is sufficient for general discussions on shear.

 

[akela]

Originally Posted By: orlzx6r
Originally Posted By: tinmanSC
...
If you want to compare 5W VS 10W, you gotta look at cold numbers.
http://www.bobistheoilguy.com/visc.html

There is some bad information with this. A 5W-* or 10W-* does not start with a 5 or 10 weight oil. The first number is cold pumpability rating (the W stands for winter not weight).


Oil formulators can use multiple basestocks plus VII to create the desired oil. IF they left out the VII it's hard to say what SAE weight you would have.

Thanks everybody for the replies. Lots of food for thought. I see now, I was confused by "oil 101", which made me think that numbers before and after "w" represent the same units. Apparently not... cold pumpability tells us very little how the oil will behave at operating temperatures, even if we assume that it's pure dyno base.