Usually, simply following the printed directions is a good place to start... ;D ;D

I usually carefully apply a decent spray of the oil from about 4 inches away down the outside of each outer pleat in the element, then let the filter set a couple of hours to allow the oil to spread throughout the material - then check to see if there are any obvious thin or missed areas that need touching up - it's better to apply one or more THIN applications, than one TOO HEAVY one that leaves oil dripping off the filter...

Never had the slightest problems doing it my way...

 

The &quot;problem&quot; with oil in the intake tract, is that it can coat the insides of the intercooler, and reduce it's efficiency - plus, the oil coating can attract and collect dust, which makes the problem even worse...<br><br>As to what's the purpose of the oil, see the above - the oil - which in the case of the K&amp;N is NOT simply &quot;oil&quot;, but a special oil-BASED solution that is tacky/sticky in composition, and is applied to attract and hold dirt and other contaminents as they pass by in the airstream - the makeup of the K&amp;N, as well as the &quot;oiling&quot; process, allows them to hold far larger percentages of contaminents, while still functioning efficiently and passing high volumes of air...<br><br>Lots of folks don't like the requirement of occasionally handling and cleaning the K&amp;N's, and there's always the few who experience leakage problems past the filter due to poor installation or defective filter housings - the same things happen with stock paper filters - folks are just less aware or sensitive to the problem when it's a paper filter doing it... ;D ;D