Originally Posted By: aquariuscsm
Garak,any advantages/disadvantages to running an HDEO 15W40 over a PCMO 10W40 in a car that originally specd an SJ rated oil (my 300ZX)?
I'd say yes and no - way to go out on a limb, eh? You're using a synthetic 10w-40, so you won't have the problems of the "garbage" 10w-40 conventionals that frightened GM in the past. We really can't say anything about anti-wear levels, because I don't know what Syntec's 10w-40 levels are like versus a variety of HDEOs out there; from a specifications standpoint, they have equal footing in what they can choose for phosphorus, for example.
Your climate gives you a pile of choice, really. If it were me, particularly in your climate and if I were stuck on using a synthetic, I'd be torn between something like an A3/B3 A3/B4 oil (i.e. M1 0w-40, Castrol 0w-30 or 0w-40) or an E7, E9 5w-40 HDEO (like the Delvac 1 I'm using; Castrol also has such offerings if you prefer Castrol; Shell and Chevron have their versions too, among others).
If I were using conventional, given the manual specifications for your vehicle, I would be grabbing a 15w-40 HDEO without question, with a 10w-30 HDEO not outside the realm of possibility, either.