You've all seen this one before that was lifeted from a Mobil blending guide...again,
not a recipe book, but some of the best information that we've got
And we "know" that the blending calculators tell you what you want to know regarding a mix, but as I've repeatedly warned, the beaviours need to be linear in response, and additive to give you the same number as a calculator.
Yep, the calculators are based on well known rules/laws for blending basestocks, but my query has always been how well they do with already formulated oils that AREN'T just simple basestocks.
A few minutes of messing should get you across the line that viscosity Modifiers, due to their nature have a lower impact in terms of viscosity modification in heavier basestocks, as the intrinsic shear stresses are higher in a higher viscosity basestock.
And typically (and especially so the 0W grade) the higher the high temperature grade, the lower the base oil viscosity, and the more VII.
Today while messing around with headlight bulbs and cabin air filters, I was pondering what mixing a monograde with a multigrade netted...whether the blending calculators made sense in those worlds, when you aren't averaging basestock viscosity and VII concentration in the traditional multigrade format, but are instead diluting with an entirely, and much thicker basestock.
So messed around with the Mobil numbers...
* the Base Oil (BOV) viscosity, particularly with the 0Ws drops with increasing high temperature grade.
* There's more (obviously) VM additive to get the higher high temperature grade with the lower BOV (shows in NOACK in the original table)
* that the simple ratio of final KV100 on calculated BOV for a given VM treat rate drops, as it should with the increasing shear stresses in the thicker base-stock.
* that within the grades (e.g. 0W, mixing say a 0W20 with a 0W40 puts the BOV AND the VM treat rate about and approximately into the 0W30 grade)...near enough for Government work anyway.
So then looked at simply adding SAE30, and SAE40 in a 1:4 ratio...look at what that does to the BOV, as it's heavier than any of them as it stands...SAE30 is 20% thicker than the calculated for the 10W60 BOV.
VM percentage reduction obviously proportional...and I can't calculate anything from it with regards to final product, but if you poke around looking at the KV ratios, and the VM rates, and the BOV, you can get a feel for what the world looks like.
Mix them 50:50 like the last lines, and ot's even more different.
My "feelings" from this (not postulating anything as facts) are that due to the non linearity in behaviour of VMs and Basestock viscosities, adding SAE30 Newtonian actually is likely to thicken almost anything, particularly ILSAC even the wide range 40s.
A 0W30/SAE30 mix could well be knocking on, or nudging in to 40 grade territory...
The 10W60 is likely going to be thinner for sure...but with half the VM treat rate, would it be more shear stable and useful ?
Just a thought experiment, and interested in the views of the guys who actually build (or built) oils for a living