The Nissan manual for the S15 2.oLtr recommends 10w-30 for temps above -4F. However on the chart it shows 5w-30 from -22F to +59F and 10w-30/10w-40/10w-50 from -4F to 104F+. It also says 5w-30 should only be used in extremly cold conditions on turbo models, which matches chart. Forgive me if I'm wrong here, but at operating temperature isn't a 5w-30 and a 10w-30 the same? As no mention of synthetics is made I would gather these relate to dino oils. BTW: Where I live it only gets down to about +14F (0C) a couple of times a year in the morning. What are board members thoughts on this? If the 5w is a concern, why does the dealer use a dino blend 7.5w-30 and M1 5w-50?