[MrTookies]

Hi there,

This is the first time I am replacing the air filter on my 2011 E90 after warranty/maintenance plan... and I'm a little surprised when I opened the the Air Filter there was the OEM filter on one side and some other gray/white filter on the other side that doesn't seem like it can be replaced? On my F15 I only have one filter... Why are there 2 filters or if it's not a filter what's the purpose?

Top old OEM middle new KNN and bottom not sure what that is...


Thanks

[BimmerNugget]

The grey filter is the "charcoal filter". It's for emissions purposes, suppose to trap gas vapors or something like that.

It's not removable, but many of us (including myself) cut out that charcoal filter also known as the "charcoal delete".

People do the "charcoal delete" in an effort to gain horsepower and a little more noise. I have yet to realize any such gains. Personally, I would've just kept the charcoal filter in place. Waste of my time to cut it out with nothing to show for.

[MrTookies]

Originally Posted by BimmerNugget

The grey filter is the "charcoal filter". It's for emissions purposes, suppose to trap gas vapors or something like that.

It's not removable, but many of us (including myself) cut out that charcoal filter also known as the "charcoal delete".

People do the "charcoal delete" in an effort to gain horsepower and a little more noise. I have yet to realize any such gains. Personally, I would've just kept the charcoal filter in place. Waste of my time to cut it out with nothing to show for.

Thank you for that reply! That makes sense, or not lol. I was just very surprised to see a second filter when I opened it up.

Just wondering if over time that charcoal filter will get "plugged up" and I might have to just cut it out.

[david in germany]

Since it looks like you are installing a K&N oiled filter, it will get clogged up eventually. The oil from the K&N will transfer to the charcoal filter that is designed to always stay dry (not good if oily). Do the delete or get rid of the K&N before it contaminates.

[MrTookies]

Originally Posted by david in germany

Since it looks like you are installing a K&N oiled filter, it will get clogged up eventually. The oil from the K&N will transfer to the charcoal filter that is designed to always stay dry (not good if oily). Do the delete or get rid of the K&N before it contaminates.

Thanks, that's what I thought. To delete it I can just simply cut it out or do I need to do some FDL coding as well for some reason?

[Efthreeoh]

Get rid of the K&N. They are a waste of money and a PIA to clean.

[MrTookies]

Originally Posted by Efthreeoh

Get rid of the K&N. They are a waste of money and a PIA to clean.

Not sure where that's coming from, why do you say that... I have been running KNN in other bmw's for years, love them, never had a problem and the cleaning is super easy, only takes a few minutes. Spray on cleaner -> rinse off -> let it dry -> spray on oil -> done.

[Efthreeoh]

Originally Posted by MrTookies

Not sure where that's coming from... been running KNN in other bmw's for years, love them, and the cleaning only takes a few minutes. Spray on cleaner -> rinse off -> let it dry -> spray on oil -> done.

It's coming from about 20 years of experience on 5 different vehicles. K&N filters provide no performance gains in either HP or fuel mileage. I switched back to OEM filters for all my vehicles several years ago. I keep detailed MPG records for every vehicle, never realized a gain in fuel mileage.

$14 remove dirty filter, throw in trashcan, open new filter box and install. 5 minutes. Most people keep their car to 100,000 to 150,000 miles, which is just 2 - 3 airfilters, so $50 in cost and no labor to clean, wait to dry and oil a K&N.

[MrTookies]

Originally Posted by Efthreeoh

It's coming from about 20 years of experience on 5 different vehicles. K&N filters provide no performance gains in either HP or fuel mileage. I switched back to OEM filters for all my vehicles several years ago. I keep detailed MPG records for every vehicle, never realized a gain in fuel mileage.

$14 remove dirty filter, throw in trashcan, open new filter box and install. 5 minutes. Most people keep their car to 100,000 to 150,000 miles, which is just 2 - 3 airfilters, so $50 in cost and no labor to clean, wait to dry and oil a K&N.

Gotcha, well... I guess that works for you... where I live, I like cleaning mine about every 25k and hopefully my car last a lot longer than 150k.
... and the KNN is about $50 as well...

[Efthreeoh]

Originally Posted by MrTookies

Gotcha, well... I guess that works for you... where I live, I like cleaning mine about every 25k and hopefully my car last a lot longer than 150k.
... and the KNN is about $50 as well...

I guess I'm trolling here, but really, my issue with them is the re-oiling process is critical to good filtration performance. The automated manufacturing process precisely oils the cotton element at the factory. Re-oiling the filter after cleaning it by the home mechanic can be uneven and reduce the filtering performance. To me, the risk of poor performance once it's been cleaned and re-oiled is not worth the cost and effort to use a K&N. I forget what the cleaning kit costs ($10 - $15?), but add that into the price of the filter and I just don't think there is any cost benefit to a using a reusable airfilter. I got tired of waiting several hours for the filter to dry and then re-oil, even though I have multiple cars to drive. I mean, if one sees a gain in MPG, then the filter may pay for itself, but MPG gains are imperceptible. Then there is always the risk of contaminating the MAF...

[MrTookies]

Originally Posted by Efthreeoh

I guess I'm trolling here, but really, my issue with them is the re-oiling process is critical to good filtration performance. The automated manufacturing process precisely oils the cotton element at the factory. Re-oiling the filter after cleaning it by the home mechanic can be uneven and reduce the filtering performance. To me, the risk of poor performance once it's been cleaned and re-oiled is not worth the cost and effort to use a K&N. I forget what the cleaning kit costs ($10 - $15?), but add that into the price of the filter and I just don't think there is any cost benefit to a using a reusable airfilter. I got tired of waiting several hours for the filter to dry and then re-oil, even though I have multiple cars to drive. I mean, if one sees a gain in MPG, then the filter may pay for itself, but MPG gains are imperceptible. Then there is always the risk of contaminating the MAF...

I get what your saying, and that's fine - everybody their own. The thread question really wasn't for "should I use KNN or OEM?", though...

Never had any issues with MAFS...

Also not gonna throw the filter away after I already purchased it!
Your comment would have made more sense if you said something like "next time don't use KNN, waste of money" or whatever. Just throwing is away doesn't make sense...

[Efthreeoh]

Just one more data point...

I bought my Z4 in December 2014; it was 6 years old . It only had 23,000 miles, so it was about 3,800 miles per year (i.e. it sat a lot). In August 2015, sorta by accident, I replaced the airfilter; I was actually replacing the cabin airfilter but the parts guy at the dealership brought out the engine airfliter as well so I bought it. Anyway, when I went to change the engine airfilter, I found a large mouse nest inside the airfilter housing (thanks CarMax...). I'm assuming a mouse moved in during the previous owner's time of ownership. The filter was literally half-clogged with mouse nest material. You'd think I'd have noticed poor engine performance and poor fuel economy. Looking at my MPG data as I write this: 34 fuel fills before the new airfilter shows 27.8 average MPG; 34 fuel fills AFTER the filter change the MPG average is 27.4 MPG. The point is, most cars are designed with far more that adequate airfiltering capacity.