for a hot climate which oil is better 5-40 or 5-30
5-40 would be better for the hotter weather as the 40 represents a higher viscosity when heated. Problem is, what does your BMW's owner's manual say? If it has any kind of warranty you may void it by using the wrong oil. Try a synthetic blend of full synthetic. They will give you the performance that you are looking for.
I would use 5w40, as it's thicker and will probably offer a little more protection than 5w30 in higher temperatures.
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