Originally Posted By: SR5
I always thought 10W was good to 0F or -18C
That was before the SAE change to the cold weather performance criteria. For some years now, in terms of cranking, 15w is rated down to -20C / 0F, while 10w is rated down to -25C / -15F. Pumping is tested at 5C/10F lower temps for each.
A synthetic 10w might just miss passing the 5w specs too at -30C/-35C...