GTL = higher PVC = a lot less wear says Chevron

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For what it's worth, I played around quite a bit with PVC's many years ago when I was trying to understand what made oils tick. Are they real in the sense that they reflect an actual scientific 'thing'? I'm not an academic tribologist so I'll say yes just to be polite. Are they simply an artifact resulting from how you combine various other inputs? Hmmm, as an oil formulator... I sort of suspected they were. Are PVC's useful in the oil formulator process? This I think I can answer and the answer is emphatically no!
In my experience, you should always be suspicious of what gets written in patents (apart from the ones I wrote which were fine!)...
 
Originally Posted By: Gokhan
GTL is not really Group III, despite currently being classified there for lack of a new API group. According to the patent, GTL even beat Group II in PVC, which has the highest PVC among common non-GTL mineral and synthetic base stocks.

One thing that is to be careful about here is that the patent claim applies to high temperatures, such as 130 C or 150 C. PVC for GTL, similar to PVC for Group III/III+, is probably not very high at 100 C. However, patent claims that the sensitivity of the PVC to temperature is small in GTL (high "PVC index") and GTL eventually wins in PVC at high temperatures, as PVC decreases less with temperature than for Group II. Combine this with a very high VI for GTL, you get a high viscosity under extreme-pressure and high-temperature conditions, resulting in a thicker EHL film (higher oil-film strength).

But then for Group IV (PAO), which has a similar molecular structure to GTL, "PVC index" is probably also very high and despite a low 100 C PVC, you get the same effects for PAO at higher temperatures, and chances are that the arguments in the patent not only apply to GTL but also to PAO.

So, this patent still cannot say whether a GTL base oil is better than a PAO or Group III+/PAO-blend base oil, as the comparison base stocks are Group II. Therefore, the question of Mobil 1 vs. Pennzoil Platinum with PurePlus remains unanswered.
 
Of course, though, a patent isn't a referenced work, much less a scientific paper or peer reviewed. While I would assume that a company like Chevron wouldn't waste time patenting something idiotic or false or useless, the patent system itself doesn't preclude that.
 
Apple would patent the human finger if they thought that it would preclude someone else using touchscreens.
 
I used to work for one of the US oil majors and they employed a bunch of PhD's to patent any old rot! Anything that might help block someone else's patent or otherwise muddy the waters was considered fair game. When patents are talked about as 'ammunition', you know the system has gone skewiff...
 
Maybe I could patent using non-motor oil related testing regimens for motor oil, and see if I can send out some billing each time we see improper testing procedures used.
wink.gif
 
Originally Posted By: Gokhan
One thing that is to be careful about here is that the patent claim applies to high temperatures, such as 130 C or 150 C. PVC for GTL, similar to PVC for Group III/III+, is probably not very high at 100 C. However, patent claims that the sensitivity of the PVC to temperature is small in GTL (high "PVC index") and GTL eventually wins in PVC at high temperatures, as PVC decreases less with temperature than for Group II. Combine this with a very high VI for GTL, you get a high viscosity under extreme-pressure and high-temperature conditions, resulting in a thicker EHL film (higher oil-film strength).

But then for Group IV (PAO), which has a similar molecular structure to GTL, "PVC index" is probably also very high and despite a low 100 C PVC, you get the same effects for PAO at higher temperatures, and chances are that the arguments in the patent not only apply to GTL but also to PAO.

So, this patent still cannot say whether a GTL base oil is better than a PAO or Group III+/PAO-blend base oil, as the comparison base stocks are Group II. Therefore, the question of Mobil 1 vs. Pennzoil Platinum with PurePlus remains unanswered.

The main deficiency of this patent is that they compared GTL only with Group II. Group III and Group IV were not included. Since GTL is very similar to Groups III, III+, and IV, falling somewhere between Group III+ and IV (call it Group III+++ if you like), I expect that Group III+ and IV will show similar effects to GTL, namely a high "PVC index" (low temperature sensitivity of PVC) and a therefore high oil-film strength (thick EHL film) at high temperatures (130 C, 150 C, etc.).

Nevertheless, the interesting result in this patent is that GTL beats Group II in high-temperature oil-film strength (high-temperature PVC), despite Group II having a much higher PVC at 100 C than other base stocks.

Therefore, the main conclusion of this patent is that synthetic oil has the last laugh when it comes to PVC (oil-film strength), having higher oil-film strength (higher PVC) than conventional (Group II) at high temperatures of interest (130 C and above). This is an extremely interesting result saying that synthetic oil can indeed offer more wear protection due to its higher PVC (higher oil-film strength) at high temperatures (130 C and above).

The patent does nothing in comparing GTL to Group III and Group IV. Therefore, the question of which synthetic base stock is better is not answered in this patent, and we don't know whether the base stock of Mobil 1 (Group III+/IV/ester blend) is better than that of Pennzoil Platinum with PurePlus (GTL) vice versa.
 
Originally Posted By: Gokhan

The patent does nothing in comparing GTL to Group III and Group IV. Therefore, the question of which synthetic base stock is better is not answered in this patent, and we don't know whether the base stock of Mobil 1 (Group III+/IV/ester blend) is better than that of Pennzoil Platinum with PurePlus (GTL) vice versa.


OK I'll play dummy one more time to try and close the loop on my earlier questions. Recognizing that this patent has also not addressed the question of Group V, ester-centric formulations, is it still correct to say, as you have earlier, that esters are fundamentally hobbled in comparison to the other groups in terms of film strength/PVC? And, is the HTHSv metric not relevant to lubricant comparison discussions other than atmospheric pressure ones given that our BITOG concerns always center on surfaces under pressure?
 
Originally Posted By: DeepFriar
Originally Posted By: Gokhan
The patent does nothing in comparing GTL to Group III and Group IV. Therefore, the question of which synthetic base stock is better is not answered in this patent, and we don't know whether the base stock of Mobil 1 (Group III+/IV/ester blend) is better than that of Pennzoil Platinum with PurePlus (GTL) vice versa.

OK I'll play dummy one more time to try and close the loop on my earlier questions. Recognizing that this patent has also not addressed the question of Group V, ester-centric formulations, is it still correct to say, as you have earlier, that esters are fundamentally hobbled in comparison to the other groups in terms of film strength/PVC? And, is the HTHSv metric not relevant to lubricant comparison discussions other than atmospheric pressure ones given that our BITOG concerns always center on surfaces under pressure?

HTHSV, PVC, VI, and PVCI ("PVC index", analog of VI for PVC) are all crucial parameters in determining wear, along with the additive package that includes AW/EP/FM additives, detergents, etc.

However, this patent claims that PVCI for synthetic oil (at least for GTL) is better than for conventional oil, therefore PVC for synthetic oil eventually exceeding PVC for conventional oil at some high temperature (130 C or above). Esters, PAOs, Group IIIs, etc. have a lower 100 C PVC than Group II but they may actually have a higher 130+ C PVC. Therefore, I'm not worried about the PVC for synthetic base stocks anymore, including esters. Synthetic oils in addition tend to have better VIs, helping even more for high-temperature oil-film strength along with PVC.
 
Originally Posted By: Gokhan

However, this patent claims that PVCI for synthetic oil (at least for GTL) is better than for conventional oil, therefore PVC for synthetic oil eventually exceeding PVC for conventional oil at some high temperature (130 C or above). Esters, PAOs, Group IIIs, etc. have a lower 100 C PVC than Group II but they may actually have a higher 130+ C PVC. Therefore, I'm not worried about the PVC for synthetic base stocks anymore, including esters. Synthetic oils in addition tend to have better VIs, helping even more for high-temperature oil-film strength along with PVC.


Thanks for that, it helps me understand it better. Does this also mean that the HTHSv metric is a wobbly one at best for the poor layman given that PVC most closely resembles the real world in terms of actual working viscosity?
 
DeepFriar,
HTHS holds for hydrodynamics, like bearings pistons mid stroke and the usual stuff.

EHD is usually things like roller bearings, and some cam issues.

The usual cam "fixes" are additive based, not EHD.
 
I had noted that the earlier referenced study, not the patent filing, was for roller bearings and gears. If I understand you correctly the HTHS metric is still valid for the majority of things we are concerned with. Still, if GTL has the greater "carrying" ability for extremely high pressure that would be an interesting new twist, at least to me.

Maybe we can get our future lower friction/higher MPG from GTL and roller bearing crankshafts, et al. Just kidding.
 
Originally Posted By: DeepFriar
Originally Posted By: Gokhan
However, this patent claims that PVCI for synthetic oil (at least for GTL) is better than for conventional oil, therefore PVC for synthetic oil eventually exceeding PVC for conventional oil at some high temperature (130 C or above). Esters, PAOs, Group IIIs, etc. have a lower 100 C PVC than Group II but they may actually have a higher 130+ C PVC. Therefore, I'm not worried about the PVC for synthetic base stocks anymore, including esters. Synthetic oils in addition tend to have better VIs, helping even more for high-temperature oil-film strength along with PVC.

Thanks for that, it helps me understand it better. Does this also mean that the HTHSv metric is a wobbly one at best for the poor layman given that PVC most closely resembles the real world in terms of actual working viscosity?

The answer lies in the fundamental curve of lubrication -- Stribeck curve:

image1d84afeda2c2c4f2e907b6e7ef22ccbc5.png


There are three regions in lubrication, and elastohydrodynamic lubrication (EHL) overlaps with two of them and covers a large portion of the lubrication curve. Therefore, EHL, where PVC (oil-film strength) plays an important role, is important for all engine components, including journal bearings.

The curve basically says that if you can keep the viscosity (n) high, and/or the speed (V) high, and/or the pressure (P) low, you will be in the hydrodynamic lubrication (HL) region, in which there is a thick oil film seperating the moving parts. HL region is the same terrifying phenomenon of hydroplaning of a car, where the car completely loses tire-to-road contact and starts flying on the water, which is caused by driving too fast on water -- hence the usefulness of the Stribeck curve.

So, keep your viscosity (HTHSV) high, load (pressure) low, and RPM high, and you will be fine. However, this is not always practical. For example, there will be cases where you will experience high loads and/or low RPMs, and your bearings will enter the EHL region. Then, PVC (oil-film strength) becomes important.

Also, in the valvetrain and parts of the cylinders and rings, the pressures will always be high because of the inherent geometry, as you don't have the luxury of a large smooth matching surface as in the journal bearings. Therefore, valvetrain and parts of cylinders and rings always run in the boundary lubrication and mixed lubrication regions because the pressures are always high between sliding components due to their smaller surface area.

In summary:

(1) Keep you HTHSV high enough so that you spend as much time in the HL region (rightmost part in the curve) as possible, where there is no metal-to-metal contact at all (like no tire-to-road contact during hydroplaning). The only downside to this is that as you can see in the curve friction increases slowly as you move further right into the curve. This is not due to metal contact but because of the internal friction of the oil. There is no engine wear caused by that by you lose fuel economy if you make HTHSV too large and you are needlessly too far right into the curve.

(2) EHL regime and therefore PVC (oil-film strength) is always crucial in any part of the engine, including journal bearings, while being a lot more crucial in the valvetrain and parts of cylinders and rings, where you are always in the BL and ML regions. (Note that in the BL region, AW/EP/FM additives are crucial.) Therefore, always choose an oil known to exhibit low wear due to its higher-quality base stocks. You don't necessarily need a synthetic oil. Nevertheless, the Chevron patent claims that with a synthetic (at least with a GTL), you have a higher high-temperature (130+ C) PVC (higher oil-film strength, thicker EHL oil film) and are better off in the EHL regime.

I hope this covers it all!
 
I'm weary of the same tired old charts being posted. And I'm not sure they're even correct. An article I read on machine lubrication website says EHL is a subset of hydrodynamic and not boundary.
 
Originally Posted By: turtlevette
I'm weary of the same tired old charts being posted. And I'm not sure they're even correct. An article I read on machine lubrication website says EHL is a subset of hydrodynamic and not boundary.

Stribeck curve is correct and fundamental to lubrication.

EHL is not in boundary lubrication. It falls between mixed lubrication and hydrodynamic lubrication and overlaps with both. See the Stribeck curve above.
 
Originally Posted By: Shannow

Has some stribeck stuff, and where manufacturers are headed with lubes and economy.


Will do thanks.
 
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