Most 20 wt oils shear down to a 10 wt in service?

[CATERHAM]

The HTHS viscosity of most 20wt oils is 2.6 cP.
That's the minimum spec' for a virgin 20wt oil, consiquently even a small amount of shear, say 5%, will drop the oil out of grade as far as the HTHS vis is concerned.

I know the SAE grading system allows for a certain amount of shear but how many people would buy an oil grade knowing it only just meets a grade's requirements as far as the kinematic 100C spec' is concerned?

With regard to kinematic viscosity, it's a virtual impossibilty for a 20 wt to shear out of grade but it's the HTHS vis that counts as far correlation to the oil's actual operational viscosity in an engine at temperature.

10% to 15% shear is not uncommon with most oil, so I'd say most 20 wt users are running a 2.2 cP to 2.4 cP oil and therefore would only qualify for the new spec's of a 10 wt oil.
Is that anything to be concerned about? I don't think so, as a 2.2 cP to 2.4 cP oil is just fine for most applications.

It's the psychology of it. If most people realized they were only running a 10 wt oil they'd just freak!

 

[HTSS_TR]

Originally Posted By: CATERHAM
It's the psychology of it. If most people realized they were only running a 10 wt oil they'd just freak!


Not me. I already use two weight thinner in '00 E430. It has Synpower 5W20 instead of recommended M1 0W40. The engine is much quieter with thinner oil, if it thin down to 5W10 so be it.

 

[ekpolk]

The unjustified leap in your logic is the statement, "10% to 15% shear is not uncommon with most oil, so I'd say most 20 wt users are running a 2.2 cP to 2.4 cP oil and therefore would only qualify for the new spec's of a 10 wt oil." I'd want to see some actual UOA showing such a decline in the 20 range before I'd take it as a given.

 

[modularv8]

It doesn't work that way. The oil may shear out of grade in regard to KV, but HTHS doesn't really change. The average molecular weight of the base fluid decreases with shear and leads to a lower KV. However, the compressibility of the fluid changes insignificantly ( more a function of oil contamination, fuel, etc.) HTHS is a Pressure/Temperature dependent function and its numerical value has units of pressure. The HTHS spec of new oil changes very little (not linear) as the used oil shears.

 

[CATERHAM]

I agree with your statement that HTHS vis is Pressure/Temperature dependant.

That's why I said HTHS vis correlates with the operational viscosity in an engine as measured by it'd oil pressure. K'vis does not. But oil does indeed shear as measured by the HTHS method. Anyone who has an oil pressure gauge equipped car, or better still an oil temp' gauge as well will have noticed this.

To give a recent example. I'm currently running the Toyota 0W-20 in a car of mine. This high VI oil's viscosity as determined by oil pressure dropped about 8% in as little as 300 miles and stabilized at that point. Assuming the virgin oil HTHS vis was 2.6 cP I figure it has dropped to about 2.4 cP currently. Contamination nor fuel dilution have had a chance to play a part in the viscosity drop.

 

[CATERHAM]

Originally Posted By: HTSS_TR
Originally Posted By: CATERHAM
It's the psychology of it. If most people realized they were only running a 10 wt oil they'd just freak!


Not me. I already use two weight thinner in '00 E430. It has Synpower 5W20 instead of recommended M1 0W40. The engine is much quieter with thinner oil, if it thin down to 5W10 so be it.


I'm a bit more conservative than yourself. I'm running a 5W-20 in my Bimmer but it's 50% RL 5W-20 with it's HTHS vis of 3.3 cP so the net HTHS vis is about 3.0 cP; equivalent to a light 30wt oil.
On top of that the oil temp's never hit's even 90C nine months of the year and rarely exceeds it in the summer. Consiquently I figure my safety margin is pretty big.

 

[Audi Junkie]

20 won't sheer too bad since it's built up from very thin basestocks.

 

[ekpolk]

Originally Posted By: CATERHAM
...To give a recent example. I'm currently running the Toyota 0W-20 in a car of mine. This high VI oil's viscosity as determined by oil pressure dropped about 8% in as little as 300 miles and stabilized at that point. Assuming the virgin oil HTHS vis was 2.6 cP I figure it has dropped to about 2.4 cP currently. Contamination nor fuel dilution have had a chance to play a part in the viscosity drop.



OK, how did you determine this to be fact? All things being equal (and I know they rarely are), a multi-vis that relies heavily upon VIIs to achieve its rating will probably behave very differently than one that derives its properties from the inherent naturally high vis index of a good syn fluid.

More info needed...

 

[JAG]

Originally Posted By: CATERHAM
To give a recent example. I'm currently running the Toyota 0W-20 in a car of mine. This high VI oil's viscosity as determined by oil pressure dropped about 8% in as little as 300 miles and stabilized at that point. Assuming the virgin oil HTHS vis was 2.6 cP I figure it has dropped to about 2.4 cP currently. Contamination nor fuel dilution have had a chance to play a part in the viscosity drop.

Fuel dilution can stabilize, in fact spike, in a very short amount of miles driven. There have been multiple UOAs posted here with quite high fuel dilution and it turned out that the owner's sampling method was to sample after running the engine from ambient temperature and not long enough to reach normal operating temperature. That equates to around less than 20 miles of driving. So your observation of oil pressure drop and stabilization could be partly from fuel dilution. I agree it could be at least partly from mechanical shearing of VIIs.

HTHS viscosity loss vs. kinematic viscosity loss has been studied (by industry experts) and the findings have been that HTHS percentage loss is about 1/2 the percentage loss in kinematic viscosity.

 

[CATERHAM]

JAG, when I first noticed the viscosity drop I found it quite startling, and my first reaction was it must be fuel dilution. But my driving behaviour and experience with other known shear stable oils such as RL in this engine (where such rapid viscosity loss has never occurred), has lead me to conclude it must be largely due to mechanical shearing of VII's.

Thanks for the info on the relationship between HTHS vis vs. k'vis and viscosity loss. Assuming a linear relationship based on one example was rash on my part. But viscosity loss of at least 10% is common enough with many 20wt oils as a quick survey of resently posted UOA's will attest to, and that's enough to drop you down to a 10wt oil.

Is it a big deal? No, and that's my point. I know how much many members obsess over the SAE grade they choose and heaven forbid their favourite oil should "fall out of grade".

 

[CATERHAM]

ekpolk, I hope I've addressed your question.

 

[addyguy]

Gary Allan has run his Jeep 2.5 I-4 for MILES on a 0W-10 oils, and 20-weight oils before that. Of all engines that could suffer from this, and old-fashioned Jeep I-4 is right up there.

Engine runs fine, and UOA's are great. This is not an issue......

 

[modularv8]

A study in Japan (Tamoto et al) found oxidation and bearing began at HTHS 1.6 cP and below. Additionally, viscosity improvers in multigrades also protect bearings by increasing film strength. As for flat tappet cam wear, heavier weights do not significantly protect better. Protection in this domain is from additives.

 

[Gary Allan]

Quote:
Assuming a linear relationship based on one example was rash on my part. But viscosity loss of at least 10% is common enough with many 20wt oils as a quick survey of resently posted UOA's will attest to, and that's enough to drop you down to a 10wt oil.


What I think you're really saying is the HTHS may go below the "designated" threshold for SAE 20. That's not the same as saying it's a 10 weight (if there was an SAE10).

It would be very hard to shear a (typically) 8-9cSt fluid to
10w is a 20 weight fluid that meets 10w spec's without the required HTHS to allow the 20 weight designation.

 

[sbergman27]

Originally Posted By: CATERHAM
The HTHS viscosity of most 20wt oils is 2.6 cP. That's the minimum spec' for a virgin 20wt oil, consequently even a small amount of shear, say 5%, will drop the oil out of grade as far as the HTHS vis is concerned.

This question really contains its own answer. If most 20wt oils have an HTHS of 2.6, then that's what the manufacturers design for. They wouldn't design for imaginary oils that only exist on paper. "Dropping out of grade" is an artificial distinction. A bureaucratic technicality. Nothing magical happens if the HTHS happens to drop from 2.60 to 2.59.

 

[Gary Allan]

I'm sure that they factor all that into the mix of spec'ing the oil. When one is well below spec'd visc on the lower side, then you're working in uncharted territory.

 

[AEHaas]

Originally Posted By: Gary Allan
... then you're working in uncharted territory.


Some people actually live in uncharted territory.

aehaas

 

[CATERHAM]

Originally Posted By: Gary Allan
Quote:
Assuming a linear relationship based on one example was rash on my part. But viscosity loss of at least 10% is common enough with many 20wt oils as a quick survey of resently posted UOA's will attest to, and that's enough to drop you down to a 10wt oil.


What I think you're really saying is the HTHS may go below the "designated" threshold for SAE 20. That's not the same as saying it's a 10 weight (if there was an SAE10).

It would be very hard to shear a (typically) 8-9cSt fluid to
10w is a 20 weight fluid that meets 10w spec's without the required HTHS to allow the 20 weight designation.


I did mention from the outset that as far as a 20wt's kinematic viscosity is concerned it's a "virtual impossibility to shear out of grade".

There are only a couple of multi-grade 10wt oils on the market and to the best of my knowledge they all have a 100C vis in the 20wt range. RP's XPr 0W-10's 100C vis is 6.5 cSt but it's HTHS vis is something less than 2.6 cP. Honda's Japanese sourced "Ultra Green" brand 0W-10 has a 100C vis as high a 7.0 cSt and a HTHS vis of 2.2 cP (that's an American Honda estimate).

So yes I am saying if a 2.6 cP 20wt shears 10% or more it's effectively a 10wt motor oil.

 

[Gary Allan]

Just assuring that the audience realizes that it's a 20 weight fluid that cannot be called a 20 weight according to SAE. The designation "10" is an adaptation of nomenclature that is not officially recognized. RP's 0w-10 is their marketing term for their sub
Chevron Delo fluid, of that same distinction, is merely 10W. As is Mobil's, PZ, and the rest.


..but we're talking "what if's" here. I initially objected to M1's 0w-40 only being required to be a 40 grade in the bottle. It had/has absolutely no requirement to remain so .000001 seconds after the key is turned. The Euro's have to have their standards, and BY GOSH, if the ACEA spec says 40 grade ..then you had better have a 40 grade in that bottle!!! Beyond that, well, we just won't talk about it...