: Oil Residue/grease on section of Air filter on 96 N* Why?

03-19-05, 07:15 AM
I pulled my airfilter and it has around 10K miles on it. The filter looks like new except in one small section. It appears to be oil residue/grease in the middle of the airfilter. It is in a circular pattern. This is a stock non-k&n filter. (usual white filter) What causes this? I have seen this before on other cars as well.

03-20-05, 01:20 PM
You are probably just seeing a tiny bit of oil vapor from the PCV backflow "oiling" the element making the dirt in that area more visible. Also, every air box will have a characteristic flow pattern that will dirty the element in one area more than others. Unless the dirt is starting to cake onto the element it is fine. Actually, the dirtier it gets the better it filters. It has plenty of flow capacity to handle a fairly heavy load of dirt before it becomes restrictive. A little dirt buildup like you describe is perfectly normal and a good sign...shows the air cleaner is working like it is supposed to.