I'm pretty sure Mobil1 has recently changed their formulation to go to a highly refined Dino base with lots of additives, technically qualifying it for synthetic status. Lots of discussion on this topic at www.bobistheoilguy.com forums.

 

Good results as in an engine that went 110k with no problems except a bad alternator at 36k.

 

just made the switch from Castrol Syntec to Mobil 1

 

You should've oiled your alternator too to last that 110k.

 

It was a GM, what do you expect???