There was data for 17 15W-40 test oils with different VIIs and base oils in the Hugh Spikes paper. The average density correction factor for those turned out to be 0.898.

While I was calculating that, I also calculated the error in the ASTM D341 extrapolation to get KV150, which is used for the A_Harman index (effective VII content), which is in turn needed to calculate the base-oil viscosity at 150 Â°C.

I have now fully verified the validity of both the A_Harman index and base-oil viscosity at 150 Â°C calculations by accounting for the errors in the density correction factor and ASTM D341. Previously I had verified the validity by comparing against the test oils but without validating the ASTM D341 and density correction factor. So, now, we know that all the calculations are valid.

One exception is the PMA VII -- the A_Harman index and base-oil viscosity at 150 Â°C calculations don't work with this seldom-used VII type. This VII is seldom used these days because of the high solid-polymer content causing deposits.

**I have now set the density correction factor to 0.917.**While this is larger than the actual average of 0.898, it accounts for the ASTM D341 routinely underestimating KV150 in the presence of a VII. Therefore, it improves the accuracy and reliability of the calculations.

The previously used density correction factor was 0.905. The only effect of the change is to increase the VII content and decrease the base-oil viscosity at 150 Â°C for all oils, without changing the order of the oils in either quantity.

The biggest changes occur for oils with little or no VII. For example Amsoil ACD 10W-30/SAE 30 had 0.0% VII before, but now, it has 0.64% VII. While Amsoil claims it to be VII-free, it could have mPAO, which shears like a VII. In fact mPAO can be considered to be a type of VII. Of course, it could also be the result of the various approximations made. Likewise Valvoline Advanced Synthetic 5W-20 was estimated to be almost a monograde, but now, it's estimated to have a small amount of 0.88% VII.

You can read the full discussion here.

**Verification of the density correction factor and ASTM D341 against the Hugh Spikes test oils**

Finally here is the updated spreadsheet. Click on the link for the Google sheet, which you can download. As I said before, the calculation isn't expected to work for a PMA VII. Note that the base-oil (full-shear) viscosity (BO DV150 = HTFS) refers to the combined viscosity of the base oil and additive package (detergent - inhibitor (DI) package) excluding the VII. Moreover, the VII content is only an effective number equivalent to the A_Harman index, which measures the temporary shear, and it corresponds neither to the actual solid-polymer VII content nor to the content of a solid polymer packaged in a base-oil solvent.

**Estimated VII content and BO DV150 (base-oil viscosity at 150 Â°C = HTFS) of selected oils**