ST 5W30 is a 90% base/10% additive oil,is it a group 2 base?

[Alan]

Being the additive level is 10%.I wonder?

 

[JonS]

Do you mean the dino or synthetic? The dino is a group 2, and i have read that the syn is a group 4

 

[Ray H]

I'm skeptical (but not the last word) that ST "Fully Synthetic" is blended from Group IV base lube stock. For $2.99/qt. (? - someone correct me if I'm wrong on the price) no less? I also wonder about ST's dinos being Group II. (It'd be great if they are!) For 88 cents/qt. it seems more likely that it's a Group I/Group II blend. I'm not panning ST - I've used it for general and break-in driving including my latest engine. It's never given me any grief, and once my stash of Chevron Supreme is exhausted, I'll probably go back to ST. I suspect if ST dino isn't a Group II formulation, it will be once the SM/GL-4 formulations ship later this year.