cSt shearing vs HT/HS

[Danh]

As has been discussed here many times before, oil certifications typically include a minimum High Temperaure/High Shear viscosity, which also seems to be perhaps the most important spec. In the case of xxw-20 oils for instance, the HT/HS minimum is 2.6.

Using Mobil1 0w-20 as an example, the manufacturer says it has an HT/HS of 2.7 and a 100C cSt of 8.7. But UOAs frequently report a cSt of 6.5-7.0 for DI/TGDI engines. So my question is, wouldn't shearing and/or fuel dilution that reduces the cSt by such a significant amount also reduce the HT/HS below the 2.6 certification limit?

Is this apples and oranges or are many of us driving around with oil that no longer meets the spec? I realize HT/HS is most relevant for extreme conditions, but it sure tempts me to move up a viscosity grade to avoid the problem.

Thanks!

 

[Shannow]

Yep, typically the hths loss is half the KV100 loss in percentage terms.

Now usually comes the circular logic that 30s become 20s anyway (not with regularity anymore) so whatever happens to a 20 is fine

 

[Shannow]

Have been informed that people don't like my charts and excerpts, as it's a throwback to "the early days where BITOG WAS more specific and relied on science" to quote one PM.

Close enouigh for a rule of thumb if you don't know what's in your brew.

 

[Ohle_Manezzini]

8,7 minus 6.0 is a loss of 2.7 at kv100. Half of 2.7 will be the hths loss, about 1.35 hths loss. Initial hths is 2.7, minus the 1.35, results in hths of 1.35. Ow that's BAD! Wouldn't ruin bearings almost instantly at high torq conditions?
Is that 50% of kv100 loss accurate?

 

[Skid]

According to this somewhat old study (but good read): http://papers.sae.org/2003-01-1957/, the HTHS of used oil does not decrease, but goes up slightly over time.

 

[Shannow]

Originally Posted By: Ohle_Manezzini
8,7 minus 6.0 is a loss of 2.7 at kv100. Half of 2.7 will be the hths loss, about 1.35 hths loss. Initial hths is 2.7, minus the 1.35, results in hths of 1.35. Ow that's BAD! Wouldn't ruin bearings almost instantly at high torq conditions?
Is that 50% of kv100 loss accurate?


Note the use of "percentage" loss...

 

[Ohle_Manezzini]

Failing VII, how hths could increase? SAE oil became Tar?

 

[Skid]

Originally Posted By: Ohle_Manezzini
Failing VII, how hths could increase? SAE oil became Tar?

As the base oil oxidizes, the HTHS increases. Some VIIs are stable over time and shear, some aren't. I think that it's tough to generalize what VII would do, since you don't know which type and how much VII is in your oil.

The study I linked to earlier is based on actual observations of used engine oils.

 

[Ohle_Manezzini]

Originally Posted By: Shannow
Originally Posted By: Ohle_Manezzini
8,7 minus 6.0 is a loss of 2.7 at kv100. Half of 2.7 will be the hths loss, about 1.35 hths loss. Initial hths is 2.7, minus the 1.35, results in hths of 1.35. Ow that's BAD! Wouldn't ruin bearings almost instantly at high torq conditions?
Is that 50% of kv100 loss accurate?


Note the use of "percentage" loss...


Uh, got it
SO it is a 31.10 percent loss of kv100, giving 15.50 percent loss on hths, making the initial 2.7 hths decrease to 2.29 hths. Pretty low, nontheless. Out of spec for a lot of engines.

 

[Shannow]

Originally Posted By: Ohle_Manezzini
Failing VII, how hths could increase? SAE oil became Tar?


Sort of...typically they shear down, then as they oxidise, thicken up.

IIRC, the "taxi used oil" SAE paper showed some of the 20s ultimately got to around 14cst after 20k miles.

 

[Skid]

Further to the above, the study I linked to tested GF-2/GF-3 era oils in Houston, and all drains were 10w30.

 

[Carbon12]

Originally Posted By: Shannow
Have been informed that people don't like my charts and excerpts, as it's a throwback to "the early days where BITOG WAS more specific and relied on science" to quote one PM.


Don't listen to that. Keep on posting them! You are a BITOG professor!

 

[zeng]

Originally Posted By: Carbon12
Originally Posted By: Shannow
Have been informed that people don't like my charts and excerpts, as it's a throwback to "the early days where BITOG WAS more specific and relied on science" to quote one PM.


Don't listen to that. Keep on posting them! You are a BITOG professor!

+1.
Just ignore the ignorants.

 

[bbhero]

That's funny because my nickname for Shannow is The Professor.

 

[BrocLuno]

Hey Professor, if you live somewhere where it does not freeze hard and your car calls for a XW-20, why not just run straight SAE 20 ... Seems the shear issue is moot at that point

Most motors will spin easily on 20 grade on any cold night, maybe just not down in the teens or below ...

 

[Virtus_Probi]

Originally Posted By: BrocLuno
Hey Professor, if you live somewhere where it does not freeze hard and your car calls for a XW-20, why not just run straight SAE 20 ... Seems the shear issue is moot at that point

Most motors will spin easily on 20 grade on any cold night, maybe just not down in the teens or below ...


I've never looked for it, but I don't recall ever seeing straight 20 grade motor oil for sale...SAE 30 is always on the shelves in the dollar stores!
;^)
I'm sure many folks in parts of Florida, Texas, Arizona, and California (as well as many, many other US and non-US locations) would do great with straight grade motor oils.

 

[Popsy]

Isn't there some sae20 Valvoline VR1?