I would hazard a guess that it's the 15-50w stuff as I know he favours the 'Gold' labelled Motul as it doesn't actually say on the invoice.
I'm thinking it's more to do with the average temp being in the high 20degress C's with the choice of viscosity.
Thanks for the quick response & reassurance though Pleiades, it's probably about time you had your own section in the Forum to:-
'Pleiades A to Z on anything & everything in between'

And talking statistics, did you know that apparently 6 out of 7 Dwarfs aren't happy?