It might always be 95 degrees outside, but it isn't always 95 degrees inside your engine.
Multi-viscosity oil does not thin out as much as engine temp rises, so it protects better when
the engine warms up while still not putting a strain on your starter when the engine is cold.

Bill

----- Original Message -----
From: "John Brush" <jbrush@AROS.NET>
>
> 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?