Originally Posted By: jesbo
As I understand it, the N54 equipped 335i does not have an oil cooler (or may not have in the early models).
AFAIK, automatics without the sport package were the ones that did not have oil coolers. Someone correct me if I'm wrong.
Originally Posted By: MGregoir
I am not sure how, but low tension rings and high pressure injection may mean fuel is blowing by.
Rings that are optimized for low friction don't seal the combustion chamber quite as well, permitting blow-by; fuel gets into the oil and vice versa.
As far as how the high pressure injectors required for direct injection end up causing fuel dilution, the following is my understanding -- again, someone please correct me if I'm wrong. I think the spray just travels too quickly downward in the combustion chamber, and whatever pools around the piston rings just doesn't get burned effectively. DI engines in Europe don't have this problem because something about their fuels permits them to use stratified lean burn modes: the injector pulse is shaped so that it is locally rich around the spark plug and leaner around the edges of the combustion chamber, and the overall air/fuel ratio can be VERY lean (15.0 or more). Such lean operation could result in excess emissions with some of the fuels here in the US, which is why it is not used here, obviously to the detriment of oil life and fuel economy.