They are so hard to check for dirt. The hood is so heavy and those little clips are a pain in the neck to get loose. Then you have to wrestle the filter out of place and it never seems to go back in right.

Seriously I check them often and have 4-6 on hand now and change about every 8K when they are dirty. Sometimes I turn them over if they are just starting to show a spot.

 

Oiled paper actually filters the most dirt out, that's why they appear to get dirty so quickly. Check out this article off another popular forum where they did an experiment with the most popular air filters on the market - guess which one filtered the best but required frequent replacement?

Air Filtration Test - Bob is the Oil Guy

 

if you think those were expensive, trying owning one in Australia $45 AUD each = $90 per swap, and that if the dealer knows you know what you want, otherwise $120 each. Since out G37 (370GT) are all imports, they tend to really screw you!

 

I can get the NPN filters for about $5 each.. They look almost identical

 

I hope your were not serious about this...where do you think the dirt will go if you turn them over?

 

I think he's talking about rotating them, not flipping them over It's physically impossible to install them the wrong way since the seals won't line up properly.

 

yes, i rotate them. I was kidding about the difficulty but not about this. I do change them oftern and I think 8k is plenty off mileage for these and I do NOT buy them from the Stealership so I don't think they are expensive either. Clean filters do save a little gasoline, too.

 

The flipping them over part was misleading...now I understand what you are saying.