Aeroshell W100 oil is not 100 weight oil. It is 50 weight. Aeroshell
W80 is 40 weight.
The website for shell oil:
http://www.shell.com/home/Framework?..._10081019.html

Very confusing on Shell's part to name the oil the way they did.
Personally, I am a fan of multiweight oil unless you are running in a
climate where it never gets below 50 degrees for starting the airplane.
Multiweight oil gives better lubrication on cold startups. Even if you
live in a warm climate, what if you travel to a colder one, park on the
ramp and cold start?