Originally Posted by Gokhan
A_Harman indexes you calculated:
Originally Posted by OVERKILL
SpectraSyn 4: 1.011
SpectraSyn 6: 1.077
SpectraSyn 8: 1.017
SpectraSyn Plus 3.6: 0.874
SpectraSyn Plus 4.0: 0.886
SpectraSyn Plus 6.0: 0.936
What I calculated using better density correction factors listed above:
4.1 cSt: 0.981
5.8 cSt: 1.042
8.0 cSt: 0.985
3.6 cSt Plus: 0.847
3.9 cSt Plus: 0.859
5.9 cSt Plus: 0.906
Now, we don't expect these low-viscosity "neat" base stocks to temporarily or permanently shear significantly. It's true that their high-viscosity PAO (100 cSt or greater) shears to some degree with increasing viscosity and their 1000 cSt can shear like a VII, which is not unexpected as it's practically plastic. However, I would expect negligible shear for these low-viscosity PAO neat (no additives or VII, pure) base stocks.
Then, what is going on? Two possibilities:
(1) The Widman operational viscosity calculator doesn't reliably work.
(2) We are having a garbage in, garbage out (GIGO) situation by being provided bad data by Exxon Mobil.
Given the scatter in the numbers, could it be that (2) is the case, namely garbage in, garbage out?
According to ASTM D341 the values obtained from the viscosity curves can only be applied to pure hydrocarbons. This makes the application of the Widman viscosity calculator and any index based on it invalid for fully formulated motor oils. Esters, organometalic additives, inorganic additives, any molecule that contains anything other than carbon and hydrogen affects the linearity of the viscosity curve.
Originally Posted by ASTM D341
3.
Technical Hazard
3.1
Caution
...It should also be emphasized that fluids other than hydrocarbons will usually not plot as a straight line on these charts.
https://www.scribd.com/document/356620101/ASTM-D341-pdf
As for number 2, all of these indexes are based on the assumption that pure base oils don't shear. What if they all shear to some degree? The HTHS viscosity includes that shear. As OVERKILL has already stated, SpectraSun and SpectaSyn Plus are different classes of chemicals. I have no problem thinking that the longer, straighter molecules of the Spectra SynPlus will exhibit more temporary shear that the shorter, more branched molecules of the SpectraSyn.
Ed