Dragon:
Welcome to our club!As for oils:
I mostly recommend these oils (w/ the exception of the Syntec which has done poorly in VQ30 engines such as yours):
http://www.nissaninfiniticlub....229.1
But the Durablend is a known good oil.With a lower milage car staying with a 30 weight isn't a huge handicap especially if you live in a colder area.Still the 10w-40 is pretty stable and will presumably do a better job protecting during hard running to to thikcer boundary layer protection.
Of course I dont know your driving habits, so that may never be a factor and the slightly freer start-up a 4w- will ahve over a 10w- may become more important in your case.
Its difficult to predict but neither grade is a bad choice and in a younger car a 30 weight is should be ok.
Fred..
