Originally Posted By: Patman
I know that on paper the 10w30 should be more shear stable than the 5w30, and I really hate to contradict Terry, but in my experience so far with running PP 5w30 in my Corvette the viscosity has stayed nice and strong, finishing up at 11.0 cst even after 7000 miles. So in a case like that, what benefit would I get going to the 10w30? IMO, none. And since I like to stick with the same oil year round, I'm definitely better off running 5w30, especially when it can get down below 0F in the winter. So from where I sit, the 5w30 appears to be the best choice, as it can do everything the 10w30 can in terms of retaining it's viscosity, and has the edge when it comes to cold cranking performance.
WOW. Considering that oil starts out with a 100C cSt of 10.2, something is causing it to burn off or thicken up.