Thanks Murray - in my mind it'still somewhat unresolved - but very interesting and getting more so.
In essence, from what you posted, a low number indicates the characteristics of the oil at the low temperature, ie-a weight of 5 means the oil is not too thick and flows quickly and efficiently to the places where it's needed.
Conversely, the high (50) number indicates the characteristics of the oil under extremes of temperature (heat) so a high number is advantageous (one would think). Thinned oil wouldn't be doing too much of a job under heavy engine loads. (?)
I'll look up a bit of stuff tonight - wonder if NATHAN could enlighten us.
And there's the thing with synthetic v. mineral also.
Who's the expert?
ps - maybe ratings beyond certain figures are money wasted for engines under average conditions?
I think that I've posted this before - I have a number of business vehicles - 2 of which have had nothing more than regular servicing and been "knocked around" by sales reps, AND BOTH NOW OVER 500,000k,
and you wouldn't know. Tight as a drum both - always had Mobil 1
synthetic in the engines.
FRIZZLE