biodiesel fuel dilution...Evonik pesentation for STLE
Have posted before on the interaction between VII and PPDs, and some of the unhappy things that result.
This has some interesting charts, not just related to the topic of biodisel fuel dilution (some people in Oz have had sumps full of rubber from home brew biodiesel).
This chart is cool...a number of blends that contain different VIIs and DI packs (the couple of slides before this one list them and the oil properties.
An oil that's "in grade" with no PPDs, can end up out of grade with VII PPD interaction.
There's aged charts as well.
Have copped flack in the past for suggesting that cold temperature performance is the most likely to suffer with mixing fully finshed engine oils of different "design", but yet again, nasty things can happen iff the VIIs and PPDs do't play well.
That "yield stress" is part of the "W" requirements...it basically means that the oil is behaving as a semi solid "gel", that has to achieve the yield stress before (for example) falling into the void that's produced as the oil pump shifts the oil on a cold start. That's called "air binding" in the literature.