Looking at the engine operators manual of a QSB 6.7 I operate, and they list 10w30 at a lower ambient operating temperature than 5w40. Can anybody elaborate on this? Does 10w30 really have a better CCS than 5w40? Seems backward to me but there has to be some reasoning here. I trust anything that Cummins publishes, just trying to understand the reasoning. Also, what are they trying to differentiate between "All Season" and "winter conditions" RE the 10w30? They are both multi grade oils, so? Reason for my questions, I'm considering switching to a 10w30 in my 14 Ram. 15w40 is sufficient most of the time but we do get to zero and below periodically a few months out of the year. I'm thinking a conventional 10w30 would suit me well based on the included picture, even though it is not recommended in my Ram owners manual. Thanks guys.