Can someone explain this to me please? Mobil 1 15W50 has the same pour point (-45 deg) as Pennzoil 5W30. This would lead me to believe it is ok to use in cold weather. On the other hand, the viscosity would lead one to believe this would not be a good selection for cold weather. So is it ok to use 15W50 in cold weather, say as low as minus 15 degrees F? Please explain the reason as well as giving me an answer. I would like to understand this.