realisticly the 0W-40 oil only means that the oil will maintain its viscosity at lower temperatures, there is absolutly no reason that someone could not waiver from the reccommended 15w-40 in fact for some one living in the southern states a 0w oil may be more benificial to them. What people need to be wary of is running these oils in hotter climates where ambient temperatures and therefore engine temps are higher, from my experience if a good quality oil is used then it will hold up to the temperatures without loosing its lubircity characteristics. Here in the top end many people successfully use a single grade of oil in their vehicles/ machines very successfully, it is a matter of consideration as to how often is the vehicle going to be exposed to lower running temperatures. Of course though there is cost, having a multi grade oil with such a high temperature span is not going to be an in-expensive exercise as that spectrum of oil grade on the side of the bottle narrows then quite often so does the price.
