I don't run 0w anything based upon multitudes of research and for the longevity of the engine.
I read each and every website you provided and I didn't really find anything that directs to your bottom line conclusion.
Yes, in a hot weather climate you don't need a 0w-X oil because the majority of the 'cold' starts will not be really cold but this doesn't automatically concludes that a lower viscosity grade doesn't protect the engine.
From the page you provided from Castrol :
" In the past, it was common for vehicles to require higher viscosity oils such as 20W-50’s, 10W-40’s and 10W-30’s. But
as engine technology has advanced over the years, the size of engines and pathways in engine that oil flows through have gotten smaller and thinner. This has led over time to motor oil viscosity decreasing – currently 5W-30 and 5W-20 are the most popular grade and 0W-20 is the fastest growing grade.
These lower viscosity motor oils are needed to move through the thin engine pathways to protect and clean metal surfaces. Lower viscosity motor oils also result in better fuel economy"
The difference between 5w20, 5w30, and 10w30 is the temperature at which they work best, the answer depends on where you live and what the climate is.
Not completely accurate. If by climate we are talking about the difference between polar and dessert temperatures then yes, it's valid statement but the real difference between those oils is their kinematic viscosity at 40oC and at 100oC.
Everything else around the difference between those oils is in the spec sheet of each individual oil.
A 0w-X and 5w-X are almost identical in most cases (unless living in places with extreme cold) and when the engine is reaching it's operational temperatures, both oils behave like the 'X' number and not the first one. I can't understand how that is connected to anticorrosion, thermal breakdown or film protection as none of those is related to the grade or even the oil itself. All those properties are achieved by additives and not the oil itself.
But for the sake of the argument, if we are debating that 0w-20 is bad and 5w-30 is good, then why not using 20w50 instead ? it should be 'liquid gold' for the engines.
For the ones that might not be familiar, if we go back 20, 30 , 40 years , the recommended oils were 10w40 or 20w50. We are still on the same planet, same countries with the same temperatures (more or less). So why the 20w50 oil was replaced by 10w40 and then by the 5w30 ? isn't this because of both engine and oil technology advances ?