Originally Posted by Mad_Hatter
Originally Posted by sloinker
Air compressors, turbines, gearboxes......
Add Transformers.
I use to use a straight 30..30+ years ago while living in the valley of SoCal. But living up north like I do now, a multi grade is the way to go. I can just stock one lube, a 5w30, and be good year round.
Plus today's engines run hotter and rev higher, so I think the high VI of multi grades are a better fit overall???
Don't mistake a high VI to mean thermally stable and shear stable. Polyol ester, for example, has great thermal stability at 300+°F, but has a VI of just 70-80. Most straight 30, 40, and 50 grade oils are going to be more thermally stable because they don't contain viscosity modifiers. Same goes for synthetics that can achieve a multi-grade without VII.
Does any of this really matter for a daily commuter that rarely (if ever) sees over 250°F oil temps and 5000+ rpm? Nope.