K&N air filter on MB diesels
 

yo,

i just put in a K&N air filter on my 1991 300D 2.5 turbo. when i did i really didnt think i would see a difference, but was i wrong.
i had a huge improvment in highway milage (@80 mph):

28 mpg (before)
33.4 mpg (after)

nothing else on the car has changed, but i am thinking that the old air filter may have been overdue for changing, but it didnt seem that dirty. the car isnt any faster, but i definately wasnt expecting that!

was wondering if anyone else has put one of these in their diesel and what kind of results they got.

be aware
 

K&N filters are designed to be DIRTY. They filter very poorly when first shot with the oil. After they get dirty they filter as they are designed too. This may also reduce your milage back to normal too but Im not for sure.

did you put in K&N filter kit (new filter and housing) or a K&N OEM shape filter in the OEM air cleaner box?

I just converted my CA car to federal spec and was considering not using the federal air cleaner setup. Was your car any louder?

K&N's supposedly don't filter all that well, they let a lot of dirt get by, or so I've heard. Then again they are used successfully on many applications and I have used them in the past. I SOAK them with oil, so that they drip excess most of the time. I figure better safe than sorry? There is another filter company Uni that I also like. Oiled foam seems like it would do a better job than a layer of cotton. Dunno if they make a MB filter. RT

I put a K&N on my 409d with the 617 engine since the original air filter housing was damaged in a collision. The K&N was VERY loud until I put a bleach bottle over it. Now it is a lot quieter.

RW my .02 on K&N's is comming from huge amounts of talk on the subject in the 4x4 world. The talk of K&N filters not being great started with some poorly done studies. They tested the K&N BEFORE it was dirty. It is designed to be dirty and wont perform up to its potential till it is.

OEM replacement filter
no, its not any louder

I actually took my K&N out today. Looking at it I could see VISIBLE holes in the filter element, which DUH allows LOTS of dirt through. I feel a lot safer with that paper element!!

It does make the car louder out of the air intake, by quite a bit actually. It makes it resonate a lot more.

Theres a spot on the K&N that is dirty and then a spot that's not. Which doesn't make sense to me... but the damn thing didn't give me any performance difference at all (well I guess I will see when I drive it today with the paper filter) but my mileage didn't change any either. I just dont want to start burning oil sooner than I have to!

I've seen way, way, way, way too many absolutly filthy throttle body's and intake tracts from people that have been running K&N filters.

Maybe it's because there not dirty enough, maybe people don't clean or oil them right, I don't know, but I do know if it's that easy to screw up and get the kind of **** I've wiped up out of throttle bodys with my finger, pure GRIT, I don't want one.

My humble opinion..

:)

The subject of oiled-foam airfilters vs paper filters has been under debate over at dieselplace.com for a while now. There is a guy who has set up a relatively scientific test apparatus to test the various filters. The link below is to a topic with about 10 pages of the debate and test setup.

http://dieselplace.com/forum/forum_posts.asp?TID=5657&PN=2