Start Up Flow Clarified ?

I'd say 0w-40 has about twice the viscosity of 0w-20 anywhere in the temperature range

Not when you get really cold, down near where CCS is measured typically. Look at how close all these oils are for example, only the 0w-8 is ~50% thinner:
Screen Shot 2021-09-28 at 9.18.44 AM.jpg


Then compare to M1 0w-40 versions, which actually have a lower CCS visc:
Screen Shot 2021-09-28 at 9.22.43 AM.jpg
 
Yes, heavier oil takes more energy to pump. Is it significant? No. But that's part of the reason for that thinner oils are being spec'd for CAFE, those tiny incremental gains in efficiency/economy.
I referred to the article that briefly mentioned flow which is what the OP was questioning.
 
I referred to the article that briefly mentioned flow which is what the OP was questioning.
This phrasing is a bit awkward:
A will flow better and waste less energy. When these oils are pumped, they may move at the same rate, but the thicker oil will require more energy to make it move."
Actual flow volume will be the same (per the 2nd bit, assuming pump is not on the relief) but the energy required to move that oil; to make it flow, will be higher with a heavier oil.
 
Well then Chapter 2 of this website’s Motor Oil University needs a correction, as it definitely leads the reader to believe 0w-xx oils behave similarly in colder conditions.

I’m specifically referring to the halfway mark on this page: https://bobistheoilguy.com/motor-oil-102/

Where it says:
“Similarly, you could compare 0W16, 0W20, 0W30 or 0W40 as all having similar cold temperature performance, but with different ranges in high temperature performance.”
Define cold temperature. See link: https://www.selectsynthetics.com/service-classifications---grades.html#Service_Classifications
 
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