We can debate the effects of oil entering the engine all day long. It "allegedly" decreases efficiency of the ICs, causes carbon buildup in the engine, and can also contribute to knocking. I'm not sure what it does to sensors like the air temp sensor behind the throttle body.

All I can say for sure is.. No oil in my Y-pipe!! This area normally had a nasty oil buildup every time I pulled the valve out. This is after running the catch can for a few days. The past few days of driving included fats pulls, etc. I ran it extra hard today just to be sure I tested the can at max airflow.:)

In my opinion, if you have oil buildup here, you need a can. IF not, then you probably don't. I'll drain the can after two weeks and see how much it's catching. I don't expect much more than a teaspoon of oil, but you never know. I also plan on flushing the ICs, especially the driver side.

BTW, I have no idea how much residual oil enters the intake manifold thru the F-hose (or relocated pvc port at rear of manifold for >'00 models).

'00 S4 >> '08 135i.