Tim I was going to stay out of this from my last post but this is incorrect. The first number in a multi viscosity oil is the weight the oil is when it is cold. Not cold weather, but when the oil is below normal operating temperature. After the oil reaches normal operating temperature, then it changes to the second number, so 0w20 weight is 0 weight when cold and when it reaches operating temperature it is 20 weight.
If what you said about mileage were true, it would need to be 0 weight all the time, not just when cold.
The reason we are seeing all these really low cold operating weights is so that the engine can get the light weight oil pumped through it very quickly to help avoid oil starvation on startup. That's all.
I've had enough of the bickering. It's getting the OP's thread off base. So yall can keep on arguin. I am done.