Originally Posted by geeman789
Originally Posted by 2012AccentSE
... It begs the question, what would last longer if everything was identical, a car running SL 25w40 or a car running 5w30?
Neither. 0w20 is the go to oil IN ALL CLIMATES ... or so we are led to believe by more and more manufacturers.
My impression observing the relatively low-mileage smoking cars in San Jose, Costa Rica, was that they most likely suffered under-lubrication at (frequent) startups. Which might very well be due to that 25W40 that they run taking longer to reach the valve-train and the rings (through the piston sprayers). I didn't hear any engines with any evidence of knocking which would be more strongly associated with lower crank bearing wear.
Of course when the "thin vs thick" threads come up on BiTOG, usually the cited reason for using a higher viscosity is to protect against bottom end wear, ie: main crank bearings.