All this talk about fancy-schmancy multi-vis oils is just marketing mumbo jumbo. Single vis worked for decades in Grandpa's tractor and shrimp boat.
I use the O'Reilley's house brand 30-wt in everything. Its super-cheap in the 55 gal drum. Once a year, I just line up everything I own with an engine and drain them all, then pump 'em full with a hand pump.
The used stuff comes in handy to edge my yard so I never need to weed eat, and no wasting time trying to recycle that nasty crap.