Originally Posted By: Camprunner
Is there any evidence that lower cost synthetic oils (ST, Form Shell, Parts Master, Etc,) shear down faster then the so called top tier oils (M1, PP, Amsoil, etc) of the same oil weight?
The more important underlying question:
Does it matter if they do?
The lube does not exist to be self-serving. It's there to protect the engine. So if there is some shearing (moderate, not obscenely out by two grades), does it affect wear? After all, that's the purpose of the lube; to reduce wear. I've seen a lot of UOAs, and I've never seen one where shearing (or ox thickening for that matter) affects much of anything when we're only talking about typical shifts in grade. Some oils have less room for vis loss; where an engine using a 10w-40 can easily tolerate a drop to 30, I'd not want a 5w-20 to drop to a 10.
But the thing to ask is if the shearing actually causes an effect?
How will you know? Run the lubes and find out.
I doubt you're going to see much disparity in the actual protection factor; that's their job after all, and that's what you should judge them on.