This is my summary as an average auto mechanic and transmission specialist.
The problem with running motorcycle,diesel and specific race oils in todays commuter vehicles,is that it ruins the catalyst from the blowby gases.These oils have a high concentrate of zinc in them.The zinc eats the converter and allows extreme amounts of nitrates and sulfuric acid into the air we breath.Zinc is the element in oil that keeps critical components,such as cam lobe contact at the lifter,from gaulding.With the change in the way cam shafts open valves in late model engines,zinc is not as critical as it used to be.Remember mechanical fuel pumps? These changes,along with the auto manufactures warranting most converters for 120 thousand and higher miles,zinc is a big no no for the companys that back their exhaust systems.
Most motorcycle engines can be broke in with just about any type oil as long as it has a minimum concentration of 1400 ppm.Zinc is also what the friction material in most every wet clutch system needs to keep the material in shape for smooth engagement and long life.Almost every automatic transmission requires a specific amount of zinc on the frictions,which brings me to say that the reason most transmissions in our vehicles nowadays have oil that is good for 100,000 miles,do not have traditional filler tubes and indicator sticks is to keep EPA fines away from each vehicle.The fines are imposed on each manufacturers complete line of vehicles if a minimum is not met,the same goes for a minimum average mpg.These fines at only a few dollars per vehicle,adds up to millions upon millions of dollars if the standard is not met.
So,the bottom line here is it's not completely a mechanical issue with oils in todays engines.It's a green thing.
