Just because you do not see a clear line of seperation does not mean seperation didnt occur along a gradient.
VO and #2 are partially miscible but the large difference in molecular size makes it almost impossible to get complete blending that wont seperate to some extent.
With two partially miscible liquids that have been blended and allowed to stand undisturbed for some time the very top layer will be somthing like 90% of the least dense and 10% most dense. as you move down thru the liquid column the percentages will gradually change with the more dense increasing and the less dense decreasing untill the very bottom where the percentages may well be reversed. If the two liquids are similar in color you may not be able to detect this change but your engine can.