Questions about those figures I just posted....
1. If Mobil has a flash point of 392, isn't that almost dangerously low?
The Flash Point is the point at above which the "vapors" of the fluid would be ignited with an "open" flame. In other words, you have to get the lubricant hot enough to make it evaporate, and then only if there is "high" concentration of vapors, it might ignite at this temperature. Again, it only refers to the vapors of the fluid, not the liquid itself.
2. Can somebody explain to me the value of a high viscoscity index? (I know it's a trade off with too many v.i. improvers and that it's partially dependent on weight) but why, if Chevron is so great (and many of its stats ARE) is its V.I. so low?
The viscosity index (VI) refers to how the fluid changes viscosity (ability to flow) over a specified temperature range. The greater the VI, the more stable its viscosity should be over a wide temperature range. Multigrades usually have wider VI's, whereas straight weights need only be stable over a narrow temp range, so their VI's would be small. I.E., the VI must specified in terms of its context as to whether its straight or multigrade.
In general, dinos change greatly over their temp range so a lot of VII (viscosity index improver) must be added to the base oil. This applies to Group I, II, and II+ base, dino oils. Group III base, dino oils have wider or higher VI's.
True Synth's (Group IV and V base oils) are more stable over wider temp ranges so they need much less, if any, VII's.