I dare say somebody will come along later to tell me how wrong I am. But I am afraid I am a bit of an old cynic.

For the most part I suspect that all these diferent oils are a bit like all these diferent washing powders!

Its all pretty much the same stuff but in diferent coloured boxes!

Sainsburys "White Box" washing powder costs a third of the "Branded" ones and does just the same job.

There are a few cars out there that claim special needs (VW PD, Jaguar "Nicasil" and so on) that I do not feel inclined to experiment on. but for the most part I find that "Zetec" grade (5W-30 semi synth) is fine for most vehicles unless they are really knackererd and burning it. (and thats a diferent problem)

Mind, I tend to deal with older vehicles and customers who would collapse with a heart attack if I charged them £40 for a sump full of oil. In any case I have been doing this ever since one could buy the 5W-30 in big drums and have never had any problems or comeback. Indeed I have actually had people asking me what I have done to their cars cos they have never run so well before (EG people with Rover K series who had been used to using something thicker)