Automated calculator for the A_Harman index, VII content, and base-oil viscosity

[Gokhan]

I have now fully automated my A_Harman index, effective VII content, and base-oil viscosity calculator by building in the ASTM D341 viscosity - temperature relation (Walther formula) into the spreadsheet. If you want to calculate these values for an oil, you can either (a) make a copy of the Google sheet or (b) download it as an Excel file from the File menu so that you can edit and work on it: >> Estimated base-oil viscosity @ 150 °C (BO DV150) and VII content of selected oils << Input values needed (gold columns):

• oil name (info only)
• density at 60 °F (15.6 °C) (g/cm³)
• KV40 (cSt)
• KV100 (cSt)
• VI (info only)
• HTHS (cP) (high-temperature, high-shear viscosity)

Output calculated (green columns):

• A_Harman index: a measure of the effective viscosity-index improver (VII) content through the temporary shear of the oil
• VII content: effective VII content (measured by the temporary shear, not the actual solid or oil-solvent-dissolved VII content) directly given by the A_Harman index
• BO DV150 (HTFS) (cP): base-oil (plus the additive package) viscosity at 150 °C excluding the VII -- high-temperature, full-shear viscosity -- directly given by the A_Harman index and HTHS

The most remarkable output of the calculator is the base-oil viscosity (full-shear viscosity) at 150 °C (BO DV150 = HTFS), which applies to the valvetrain, timing-chain, piston-ring, and cylinder-liner wear since the oil goes through full shear in these engine components, whereas the HTHS (high-shear viscosity) applies to the bearing wear since the oil goes through high shear but not full shear in the bearings. Important notes: The base-oil viscosity includes both the base oil and detergent - dispersant - inhibitor (DDI) package. Some base oils, such as POE base stocks and high-viscosity PAO base stocks, temporarily shear like a VII and may appear as an effective VII content in the calculation. Note that I have also improved the accuracy of the calculator by accounting for the ASTM D341 underestimation of KV150 using a slightly higher density correction factor (0.917) when calculating DV150. You can read the theory and discussion in the thread below. I have recently verified the accuracy of the base-oil-viscosity calculator against the test oils in the Hugh Spikes paper, which can be found at the end of this theory thread: HTFS: high-temperature, full-shear viscosity

 

[ZeeOSix]

Gokhan - I know you've posted a lot of info in the past about all of this, but in your eyes what are the key output parameters to look at, and why when choosing an oil? We all know that higher HTHS is typically better for engine protection, but what other parameters in your data matrix could be used to rate oils from 1 to x?

 

[DrDanger]

Thanks for all the work.

 

[bbhero]

Gokhan you really are something... Extremely intelligent and always thinking about very complicated concepts... My hats off to you... I appreciate your hard work and thought processes... Very impressive

 

[Gokhan]

Originally Posted by ZeeOSix

Gokhan - I know you've posted a lot of info in the past about all of this, but in your eyes what are the key output parameters to look at, and why when choosing an oil? We all know that higher HTHS is typically better for engine protection, but what other parameters in your data matrix could be used to rate oils from 1 to x?

I use the table for information rather than rating oils. That said, for better wear protection, I would look for an oil with a higher high-temperature, full-shear viscosity (HTFS, not HTHS), which is labeled as BO DV150 (= HTFS) in my table, BO meaning base oil. That's because HTHS is usually fixed by the oil spec or oil type and the variation in insignificant -- 2.6 - 2.7 cP for a 0W-20 and 3.0 - 3.2 cP for an ILSAC 5W-30 -- but HTFS can vary greatly. For most people HTFS will make a bigger impact on wear than HTHS because HTFS has a direct effect on wear vs. HTHS acting more like an insurance against wear. Of course, HTFS and HTHS are directly related to each other through the A_Harman index; however, as I said HTFS varies a lot more than HTHS for a given oil spec or oil type as the A_Harman index varies, and you can use the table to find an oil with a significantly higher HTFS for a given oil spec or oil type. For engine-deposits control, a smaller VII content (= a larger A_Harman index) will help.

 

[Gokhan]

Originally Posted by bbhero

Gokhan you really are something... Extremely intelligent and always thinking about very complicated concepts... My hats off to you... I appreciate your hard work and thought processes... Very impressive

Thank you for your kind words, bbhero!

 

[bbhero]

No problem... Just saying it the way it is... And in your case... Your awesome... And gifted..

 

[buster]

 

[ZeeOSix]

Originally Posted by Gokhan

Originally Posted by ZeeOSix

Gokhan - I know you've posted a lot of info in the past about all of this, but in your eyes what are the key output parameters to look at, and why when choosing an oil? We all know that higher HTHS is typically better for engine protection, but what other parameters in your data matrix could be used to rate oils from 1 to x?

I use the table for information rather than rating oils. That said, for better wear protection, I would look for an oil with a higher high-temperature, full-shear viscosity (HTFS, not HTHS), which is labeled as BO DV150 (= HTFS) in my table, BO meaning base oil. That's because HTHS is usually fixed by the oil spec or oil type and the variation in insignificant -- 2.6 - 2.7 cP for a 0W-20 and 3.0 - 3.2 cP for an ILSAC 5W-30 -- but HTFS can vary greatly. For most people HTFS will make a bigger impact on wear than HTHS because HTFS has a direct effect on wear vs. HTHS acting more like an insurance against wear. Of course, HTFS and HTHS are directly related to each other through the A_Harman index; however, as I said HTFS varies a lot more than HTHS for a given oil spec or oil type as the A_Harman index varies, and you can use the table to find an oil with a significantly higher HTFS for a given oil spec or oil type. For engine-deposits control, a smaller VII content (= a larger A_Harman index) will help.

Thanks for the explanation and all the hard work you've done with all this data crunching. Looks like the 5W-30 oil I'm using has a pretty high BO DV150 value compared to other 5W-30 in your table. It also has a relatively small VII content and low Noack (from manufacturer's spec sheet). Guess I like it even more now ...

 

[OilUzer]

Gokhan, I may have asked you this question before but can't recall. Did A_Harman publish his equation or just the values? are you calculating A_Harman index based on your equations or his published equations and how close are the values? Btw I like your data and use your .xlsx as a reference and for relative comparison and my question is just out of curiosity ... Also what would be the outputs for a theoretical "pefect" oil? A_Harman: 1.0 VII: I assume 0 BO DV150: ? What's the perfect value here? 4.0? Infinity?

 

[Gokhan]

Originally Posted by OilUzer

Gokhan, I may have asked you this question before but can't recall. Did A_Harman publish his equation or just the values? are you calculating A_Harman index based on your equations or his published equations and how close are the values? Btw I like your data and use your .xlsx as a reference and for relative comparison and my question is just out of curiosity ... Also what would be the outputs for a theoretical "pefect" oil? A_Harman: 1.0 VII: I assume 0 BO DV150: ? What's the perfect value here? 4.0?

Yes, it is basically the same A_Harman index as the original one by A_Harman, the only difference being that I use 0.917 for the density correction factor (to extrapolate the density from 15.6 °C to 150 °C) in my latest version. This improves the accuracy by making up for the systematic underestimation of KV150 by the ASTM D341 extrapolation for oils containing a VII. A_Harman himself had used 0.885, which is on the low side and doesn't take into account the systematic underestimation by ASTM D341 I mentioned. A_Harman index = HTHS150 / (density150 × KV150) = HTHS150 / (density15.6 × density correction factor × KV150) To answer your question, an ideal monograde oil (it's fine if you want call it perfect) would have:

• A_Harman index = 1
• effective VII content = 0%
• BO DV150 (HTFS150) = HTHS150 (the base-oil (full-shear) viscosity is the same as the high-shear viscosity)

However, even neat base stocks -- in other words base stocks that aren't mixed with a VII -- temporarily shear to some extent, especially POE and high-viscosity PAO base stocks. Therefore, even if you have a monograde oil, A_Harman index may be smaller than 1, and the temporary shear of the base stocks may appear as the presence of a VII, even if there isn't one. Therefore, it is important to keep in mind that both the A_Harman index and effective VII content measure the temporary shear and not necessarily an actual VII content by weight or volume. Note that if, say, A_Harman index = 0.98 = 98%, then the effective VII content = (100% - 98%) / 2 = 1%, which may be right on the money for certain commercial VII types (like the ExxonMobil blend-guide oils in my table), but this is somewhat arbitrary as a manufacturer can sell even the same VII in different concentrations dissolved in a different amount of an oil solvent. So, keep in mind that it is an effective VII content directly corresponding to the amount of the temporary shear, which is what the A_Harman index measures.

 

[doyall]

The law of parsimony is not at work here.

 

[Patman]

Great work Gokhan!

 

[LubricatusObsess]

Awesome work, Gokhan. Thanks for sharing it. Gonna take me some time to digest it all.

 

[OilUzer]

I know it will be kind of comparing apples to oranges but it would be interesting to combine the 3 output columns (using a tbd formula) and come up with a relative ranking column. Rank = 1..n n = number of oils Even though the formula will for example be ranking a 5W30 against a 0W20 (apples to oranges) they are all in the same boat so the final ranking of two different 5W30's will be relative to the the best oil (rank #1). That way one can quickly determine which 5W30 got a better grade than the other bsed on your analysis. We also have to be aware of the fact that if you are dealing with 100 near perfect oils, some will rank lower and that doesn't mean they are bad. However, the negative thing about the ranking column would be additional heated discussions like there is no way oil x is better than oil y ... lol

 

[LubricatusObsess]

Let me ponder a possible conclusion from Gokhan's excellent work. If the HTFS results from the oil's he plotted were sorted in order of highest lubrication rating to lowest instead of alphabetical manufacturer, would it show that the narrower viscosity grades performed the best? i.e. - VII additives are bad in general? I'm kind of coming to the conclusion that VII additive is a lab data point, not a lubrication solution. Sure, it shows a higher viscosity under gravity flow, but when subject to actual lubrication conditions in an engine, it: 1) shear-stretches in journal bearings to the base oil viscosity, providing no thicker lubricant film 2) shear-breaks in the power cylinder ring / cylinder wall and cam / roller creating unstable sheared-down compounds that can create engine deposits So what good is a VII additive at all? IF this is the case, wouldn't we seek engine oils without VII additive? How would we know short of guessing which viscosity ranges don't need or have VII additive? I would start using synthetic with naturally high VI without additives. From my Mobil Oil days, I recall perhaps a 5W-20, 10W-30, and if there is one, a 20W-40, changed out seasonaly? I've also read about a new VII additive Shell is using that doesn't work by uncoiling with higher temp, and does retain higher vis @ higher temp w/o shead-down. Thoughts?

 

[ZeeOSix]

The VII additives are what get broken into smaller pieces from shearing which causes the oil to lose it's hot viscosity. High heat exposure can also cause the VII additive to break down and cause viscosity loss. So yes ... oils that have a relatively high VI will typically be less viscosity stable as more use it put on them. If you look in Gokan's table, most of the oils with a better A_Harman index seem to be on the lower range of VI. https://www.machinerylubrication.com/Read/29144/oil-viscosity-drops "Another way your lubricant could be losing its viscosity is through the loss or shear down of the viscosity-index (VI) improver. For example, if you are using a multi-grade SAE gear or engine oil such as a 10W-30, this oil contains an additive known as a viscosity-index improver. During use, the VI improvers can sheer down and break apart, causing the viscosity of the oil to decrease. Remember, exposure to high heat is the biggest factor in causing the sheer of the viscosity-index improver." https://www.machinerylubrication.com/Read/29842/viscosity-index-improvers "One of the major issues with the viscosity index improver additives is that they are very susceptible to mechanical shearing. For example, imagine a piece of spaghetti moving with the oil throughout an engine or in a gearbox. There are areas in the engine or gearbox that have very tight clearances and will act much like a pair of scissors cutting the spaghetti noodle (viscosity index improver molecule) into smaller pieces. Over time this greatly reduces the ability of these molecules to add to the viscosity of the fluid. "

 

[A_Harman]

Wow, Gokhan. I'm overcome.

 

[Gokhan]

The following thread, which is fairly short, explains it all. I actually saw the Hugh Spikes paper discussed in that thread, which was published a few months before my original work, only after I came up with my original HTFS idea and calculation, and it nicely verified my idea and calculation: VII (VM), shear, base-oil viscosity, HTHS, friction, and wear: State of the art The shear we are talking about here is the temporary shear, in which the VII molecules align themselves with the oil flow in high shear rates. See Figure 3 in this article. They are not permanently deformed as in permanent shear. When the high shear rate goes away, they still maintain their original shape. The temporary shear depends on the shear rate:

• In the low-shear areas such as the leak paths, the low-shear viscosity KV100 applies. The VII has the full effect in changing the viscosity, as there is no temporary shear.
• In the high-shear areas such as the bearings, the high-shear viscosity HTHS applies. The VII has a moderate effect in changing the viscosity, as there is moderate shear.
• In the full-shear areas such as the valvetrain, timing chain, piston rings, and cylinder liners, the full-shear viscosity HTFS applies. The VII has no effect in changing the viscosity, as there is very high shear.

The HTFS depends on both the low-shear viscosity and VII content, just like the HTHS does. You will see in my spreadsheet that the thicker oils have both a higher HTFS and a higher HTHS, but the spread between the HTFS and HTHS depends on the VII content. The HTHS is always higher than the HTFS. It is not uncommon for a 0W-20 to have an HTFS similar or higher than that of a 5W-30 because 0W-20 oils tend to have higher-quality base oils (such as Group III+, GTL, and/or PAO) with a lower CCS and a higher viscosity index VI, which can reduce the need for a VII and allow thicker base oils that still flow at the SAE 0W cold temperatures. Such 0W-20 oils will provide equal if not better wear protection as most synthetic 5W-30 oils in most engines. You can use my spreadsheet to estimate the HTFS and get a better idea on the wear-protection capability of an oil. By the way the Valvoline oils can be very impressive. I was calculating the HTFS for the Valvoline Daily Protection 5W-30 synthetic blend, and it's an amazing 2.4 cP, which rivals that of Euro-OEM ACEA C3 5W-30 oils, along with its very high HTHS = 3.3 cP, while still meeting the API SP/ILSAC GF-6 fuel-economy limits! It looks like we won't see many conventional 5W-30 oils anymore. However, the Valvoline Advanced Synthetic 5W-30 has got a lot thinner with API SP/ILSAC GF-6. Now, you need to update my spreadsheet for API SP/ILSAC GF-6, which was introduced eight days ago.

 

[Gokhan]

Originally Posted by A_Harman

Wow, Gokhan. I'm overcome.

Thank you, A_Harman, for your original work, which calculates the temporary shear or an effective VII content. I have extended it to calculate the base-oil (plus the detergent - dispersant - inhibitor (DDI) package) viscosity, which I call high-temperature, full-shear viscosity HTFS.