HTHS vis spec trumps the Kinematic 100C vis spec'

[addyguy]

Originally Posted By: CATERHAM
Originally Posted By: Gary Allan
Here's one point you've brought up a few times that I just can't rationalize.

You've stated that you can take any number of lubes and merely take their HTHS to determine their REAL operational viscosity. If that were the case, then VII would be a 100% waste of product. You could merely run without them ..if as you allege they have no effect on operational viscosity.

Where's the missing link in the logic for me?


Gary, thanks for your input.

I've never said VII's have no effect on operational viscosity, quite to the contrary.

Using the simply 10W-30 vs straight 30wt mineral oil example I mentioned. The 10W-30 being basically a 10wt oil with a load of VII polymers in it will of course be lighter than the straight 30wt at cold temperatures. But at 100C if the 10w-30 has just the same kinematic viscosity as the straight 30wt your operational viscosity in an engine will be lower due to the compressable nature of the polymers under stress. To compensate you will have to add more polymers thereby raising the kinematic viscosity of the 10W-30 beyond that of the straight 30wt oil. How much more? Enought to equalize their HTHS viscosities.

Adding VII's to an oil increases both the 100C k'vis spec and the HTHS vis of the oil, they just increase the 100C k'vis spec at a disproportionately higher rate to the HTHS vis.


Can I ask a fairly 'basic' question here?

I thought VII's had very little effect on HT/HS values, because at that level of 'stress', even the best VII's are 'heated/crushed' to nothing, as VII's don't react well to heat. I thought when you got to this level of measurement, you're looking at the strength of the base oil alone?

 

[Gary Allan]

Here you get into stuff that "sounds" like it belongs to a dialysis machine and perhaps injection molding too (fill in "yeah-yeah ..and 2+2 is 22"

)

 

[glxpassat]

Originally Posted By: Audi Junkie
GC has a HT/HS of 3.5cP, so does 15w-40 HD (E7)


3.5cP might be a minimum API spec for a HD 15w-40, but all of the ones I've looked at are typically around 4.3cP. I would expect GC to give better mileage.

 

[BobFout]

Originally Posted By: glxpassat
Originally Posted By: Audi Junkie
GC has a HT/HS of 3.5cP, so does 15w-40 HD (E7)


3.5cP might be a minimum API spec for a HD 15w-40, but all of the ones I've looked at are typically around 4.3cP. I would expect GC to give better mileage.


AJ is referring to ACEA E7.

 

[glxpassat]

Originally Posted By: BobFout
Originally Posted By: glxpassat
Originally Posted By: Audi Junkie
GC has a HT/HS of 3.5cP, so does 15w-40 HD (E7)


3.5cP might be a minimum API spec for a HD 15w-40, but all of the ones I've looked at are typically around 4.3cP. I would expect GC to give better mileage.


AJ is referring to ACEA E7.


I know that, but you're not going to find a 15w-40 with that low of a hths. A straight HD 30W would be around 3.5 cP.

 

[Gary Allan]

CATERMAN

Let me state that I really think you're on to something, but at my level of comprehension it is probably beyond my ability to grasp it.

You too may "see" what you're trying saying, but cannot necessarily navigate the intermediate ground to get there from here ..at least in articulating it.

..but seeing as you haven't been spanked by those of greater intellectual and technological/tribological firepower, you'll just have to bear with some of us who cite objections (should be viewed as "how do I reason this apparent hole?") that you may not yet be prepared to overrule with an proper response.

Quite often the revelation of conceptual view forms an insulated conduit that bypasses much intermediate ground. In some cases, you might truly not know how to get there.

 

[CATERHAM]

Originally Posted By: addyguy
Originally Posted By: CATERHAM
Originally Posted By: Gary Allan
Here's one point you've brought up a few times that I just can't rationalize.

You've stated that you can take any number of lubes and merely take their HTHS to determine their REAL operational viscosity. If that were the case, then VII would be a 100% waste of product. You could merely run without them ..if as you allege they have no effect on operational viscosity.

Where's the missing link in the logic for me?


Gary, thanks for your input.

I've never said VII's have no effect on operational viscosity, quite to the contrary.

Using the simply 10W-30 vs straight 30wt mineral oil example I mentioned. The 10W-30 being basically a 10wt oil with a load of VII polymers in it will of course be lighter than the straight 30wt at cold temperatures. But at 100C if the 10w-30 has just the same kinematic viscosity as the straight 30wt your operational viscosity in an engine will be lower due to the compressable nature of the polymers under stress. To compensate you will have to add more polymers thereby raising the kinematic viscosity of the 10W-30 beyond that of the straight 30wt oil. How much more? Enought to equalize their HTHS viscosities.

Adding VII's to an oil increases both the 100C k'vis spec and the HTHS vis of the oil, they just increase the 100C k'vis spec at a disproportionately higher rate to the HTHS vis.


Can I ask a fairly 'basic' question here?

I thought VII's had very little effect on HT/HS values, because at that level of 'stress', even the best VII's are 'heated/crushed' to nothing, as VII's don't react well to heat. I thought when you got to this level of measurement, you're looking at the strength of the base oil alone?


Wow, that's another couple of HTHS vis myths I hadn't heard of, so thanks or that.

Polymer based VII's actually require heat for activation, that's how they work in multi-grade oils. As mentioned they of course do increase the HTHS viscosity of an oil; no point in using them otherwise, and most of the modern VII's used today stand up very well over an OCI.

 

[Bruce T]

Caterham, you've put quite a few ideas together in an impressive way. It has generated a very good discussion, even when people disagree with you. In my opinion, these differences in opinion don't detract from the originality of your thought.

I would only say that fuel economy doesn't completely correlate with HTHS, as mentioned by Tom NJ in the first post link:

"As for the effect of these viscosities on fuel economy, most frictional losses occur in the bearings and ring/cylinder wall interface. Both of these areas are under high shear rates, so all else being equal the HTHS viscosity should correlate better with mileage than kinematic viscosity. Of course, all things are rarely equal, so friction modifiers, polar base oils, VI Improver quantity and type, engine shear rates, and temperature will have some influence on this correlation. Furthermore, if the HTHS viscosity gets too low, friction can increase as parts move into elastohydrodynamic or boundary regimes (Stribeck curve), so the correlation of HTHS viscosity to fuel economy is only valid within a range."

 

[Gary Allan]

That's why I say he's stating things under assumptions of certain "givens" or assumed constants that he has yet to express.

 

[Bruce T]

Yes, I agree with you he is on to something, but I'm not smart enough to finish assembling this very complex puzzle, either.

 

[CATERHAM]

Guys, lets not get off track here.

We're just talking about an oil's viscosity, of course there are other elements like an oil's chemistry and additives that play a role in an oil's ultimate fuel economy rating, that's why Tom said "all things being equal HTHS viscosity should correlate better with mileage than kinematic viscosity".

My point is not about fuel economy but rather the accuracy of how the viscosity of motor oil is measured.
And that the popular reliance on the kinematic 100C viscosity spec' as an accurate measure of viscosity is flawed and does not correlate well with the operational viscosity in an IC engine. The HTHS vis spec' is an accurate measure of viscosity and as it turns out correlates very well with operational viscosity.

 

[Bruce T]

We're actually on the same track as you, but we want to extend it even further. I understand Gary (for once). We're not disagreeing with your premise or the bulk of your original post, but rather saying it's worth studying and building on.

 

[Gary Allan]

Originally Posted By: Bruce T
We're actually on the same track as you, but we want to extend it even further. I understand Gary (for once). We're not disagreeing with your premise or the bulk of your original post, but rather saying it's worth studying and building on.

Yes

I don't have the horsepower to figure it on my own and am trying to get a foothold somewhere in his presentation.

I've got nowhere to go with it except where I find things counter to my current level of understanding ..and seek to have them realigned so that I might be able to keep up. They can appear as challenges.

 

[Newtonville]

I found wikipedias notes on "viscosity" interesting as well as this English site

http://www.kewengineering.co.uk/Auto_oils/oil_viscosity_explained.htm

It seems it is entering the realm of chemical engineering/fluid dynamics.

Basically I see dynamic and kinematic viscosity described, dynamic being kinematic divided by density. One is in cSt, other cP. In very complex molecules in solution with other complex molecules, or additives, tracking the density changes at temperatures, pressures, and shears would be challenging? Since HTHS test uses the same cP units as dynamic viscosity, as decribed on sites, aren't they one and the same? Is HTHS= dynamic viscosity at 150c?

Maybe Pennzoil's "adaptive molecules" are not to be made fun of so much after all.

 

[river_rat]

CATERHAM, can you post a OP vs published HTHS graph with R² correlation from Excel?

 

[Tempest]

Originally Posted By: CATERHAM

My point is not about fuel economy but rather the accuracy of how the viscosity of motor oil is measured.
And that the popular reliance on the kinematic 100C viscosity spec' as an accurate measure of viscosity is flawed and does not correlate well with the operational viscosity in an IC engine.

The only way to do this would be to measure EVERY contact area in a given engine and give it a rating. As Tom pointed out, there are too many variables to be able to put this all on a data sheet.

100C viscosity is easily controllable and repeatable. And I would guess that engine/bearing designers have the information to correlate that viscosity with actual viscosity in use. This information has been derived via decades of design work and trial and error.

Quote:
The HTHS vis spec' is an accurate measure of viscosity and as it turns out correlates very well with operational viscosity.

Can you please provide some information to show this?

 

[Tempest]

Quote:
As mentioned they (VII) of course do increase the HTHS viscosity of an oil

Yes, but not as well as oil does. There is a reason premium gear oils do not use VII. They don't deal with pressure well.

 

[CATERHAM]

Originally Posted By: Newtonville
I found wikipedias notes on "viscosity" interesting as well as this English site

http://www.kewengineering.co.uk/Auto_oils/oil_viscosity_explained.htm

It seems it is entering the realm of chemical engineering/fluid dynamics.

Basically I see dynamic and kinematic viscosity described, dynamic being kinematic divided by density. One is in cSt, other cP. In very complex molecules in solution with other complex molecules, or additives, tracking the density changes at temperatures, pressures, and shears would be challenging? Since HTHS test uses the same cP units as dynamic viscosity, as decribed on sites, aren't they one and the same? Is HTHS= dynamic viscosity at 150c?

Maybe Pennzoil's "adaptive molecules" are not to be made fun of so much after all.


Actually, dynamic viscosity is the kinematic viscosity times (not divided by) the oil's density. It doesn't equal the HTHS viscosity because it doesn't factor in the pressure-viscosity coefficients of different oil chemistries.
See the following paper, particularly page 8, which goes into some detail on the relationship between HTHS vis and dynamic vis:

http://www.kulikow.com/project/Literature/PEG-Esters/NoLowSAPEngineOil-JAI2008.pdf.pdf

 

[Tempest]

From the link:
Quote:
Table 2 shows that the HTHS is not necessary for describing the viscosimetric behavior of polymerfree
alternative engine oils and the dynamic viscosity at 150°C looks sufficient for the film thickness in
combination with the pressure-viscosity coefficient. The determination of viscosities at shear rates much
above 106 s−1 with low film heating during testing is desired for the future, as in the tribosystems “crank
shaft/Shell” and “Piston ring/cylinder liner” much higher values occur. The loss in viscosity by high shear
rates will be lowest or quasi inexistent for polymer-free formulations.

Most interesting. I knew there was a reason I didn't like VII much.

 

[Shannow]

Seconded.

We were having problems with Voith turbo couplings (10,000hp constant speed input, variable output) in the 90s.

BP made n ISO 32 hydraulic oil for these units, and and HV (High VI) ISO 32 oil for them also.

Previously the High VI oil had been chosen for it's superiority.

In service, it quickly became around ISO 24.

At that learning point, I turned right off the "knowledge" of the day that the biggest VI was always superior...15W-40 became my oil of choice (5W-40 in synth).