[arpad_m]

Originally Posted by DorkMissile

Just understand - environmental demands is what drives the research in motor oils.

One way to think about it, that with each new "generation" of oils that comes along, (API SJ to SL, SL to SM, etc....) you end up with a product that is as almost as good as the previous generation as far as lubrication goes, but contains less "dirty" ingredients (things like Zinc and Sulfur). The best oils you can buy over the counter are actually the older ones that are SJ level.


It is just that if you run SJ oils in a stock modern car, you could see issues with clogging the cats as the older ingredients tend to want to stick to the cats when hot.

A newer oil or newer API certification doesn't mean it is better at lubricating

I understand, but we are pretty much stuck between a rock and a hard place. Replacing clogged cats is expensive, deleting them is illegal and the car won't pass emissions, running the new oil is still the best we can do.

(Also, one of the advertised features of the new 0W40 is that one can run the same oil on the street and for light track duty, so I'm not 100% sure changes are solely related to emissions, but my knowledge of motor oils is very limited.)