Is the recommended 0-20 bad for engine life?

I read up on oil years ago and my general take away was that the upper number for when the engine was hot should be at least 30 if not 40 and the cold number was always too high so go as low as possible, certainly use 0 instead of 5 or 10. In general it may not make a huge difference but until now I’ve always been asking for 0-30 or 0-40. But today I was told at three different oil change shops that I had to use 0-20 because that was all they could select or that was their shop rule. I know...

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