Pacnorth...

can you please elaborate on the difference between the base oil differences between Group 4 and Group 3?

From my research and talking to a good friend who is a surfactant (the slippery stuff in oils and soaps) chemist....I've always contended that since all Synthetics are Petroleum based, the term 'Synthetic' (defined as derived from something other that petroleum stocks...ie, wood or other derived surfactants) was a bit of an advertising misnomer.....I look at Synthetics as being more like "cherry-picked" or cultivated molecules that have uniform desired characteristics....chosen within a much more narrow range than "off the shelf" oils.

The Germans had very little oil reserves during WW2....their surfactant chemists did develop "true" sythetic (i.e., not petroleum based) oils based from wood and other plant forms that they used to supplement their limited oil reserves...this is where the term originated but it had been overused in modern years.

In simple terms...Traditional motor oils are made up of a more random batch of "good" and "not so good" (but still acceptable) molecules, in use it's really the 'bad' ones that break-down first which in turn dilutes the entire sump full of oil....synthetics are 'the chosen' molecules verified through testing to hold up longer so they tend to last longer under more extreme conditions....but they are not really "synthetic" in the true sense of the word.