The differences between mult-weight and straight weight oil eludes me.

If it is always 95 degrees, what is the difference in viscosity and
protection between 20-50W and straight 50W? Does not the use of
mult-weight simply mean a thinner oil in cooler temps, and the thicker
rating when it is hotter?

I was taught that the 10-40W will be basically 10W in colder weather (temp
dependent) to make starting no problem and still be as protective as
straight 40W when it is hot.

I am ignorant of why straight weight even exists anymore. (and on a lot of
other topics as well)

I run 20-50W year round here in SLC, and have never had any trouble
starting in the winter. It ain't Alaska, but it does get darn cold <g>

Thanks for the lessons,

John