I run a K and N. I also bought it for the reusablility. BUT I did notice after I cleaned it the first time, my mileage actually went DOWN. Not that is is getting dirty again my mileage went back to normal.

 

x2. The oiled filter is also harder to clean when you get allot of dirt offroad. You can just bang the paper filter against something or use a air hose.

 

i purchased the k&n simply because the auto stores around here still do not carry a cheapo paper replacement as i have used all of my life which in my opinion work fine and are simple and effective, however i refused to pay what the stealership wanted for a stock paper filter. the reusable k&n was only few bucks more so i went with it. thus far it works fine as far as i can tell and i have actually noticed i slight improvement in my gas mileage using it. as far as any other performance enhancements from it i can tell no difference. i purchased the recharge kit for cleaning it and it is simple enough to use and seemingly will last quite a long time, like the life of the filter frankly so i figure i'm ahead in the dollar department all around vs. the paper filters. i will mention though it is worth keeping your old paper filter so that you can pop that in and keep rollin' while the k&n is drying out after washing it. one other interesting thing worth mentioning and i will shut up is that the k&n filter says right on the box that the lifetime warranty is void if filter is used in an offroad and racing situation and it is not meant for 'dusty offroad' environments which i thought sucked after buying it, but personally i don't see why this would ever be an issue given that it is washable which as toad says would be preferrable for offroad vehicles.

 

I'm not a K&N filter expert, but I would think that would affect the ability of the filter to work as well as it should.

But, regardless, I was talking about those dusty trails when you get so much dust in the intake and you need to clean it then and there. I have noticed that this hasn't been the same issue as with my old TJ. Too many variables though to say one way or another as I lived in Colorado then.

 

Paper for me. I had a K&N and a CAI on my BMW, but that won;t go on the Jeep. BMW never went off road.

 

Agreed had one on my 400ex sport atv when I had it and we did a motor rebuild on it and there was a lot of build up and "gunk" for lack of a better word in the motor. Also I know a diesel mechanic at a local ford dealership that says they see a lot of turbos ruint because of K&N filters(and others like K&N). Just my $.02 I'm no expert but I won't ever run one again.

 

My brother has a K&N replacement filter in his Nissan Titan and he drives the same place basically every day and his avg gas on his dash went from 14 to 16MPG, I'm not sure how accurate they are though.

 

i have used k&n on all my vehicles and have gotten about 2 mpg increase in each vehicle. i averaged about 100k miles on each vehicle (one was a tj) with no problems whatsoever. however, i dont believe i will be putting one on my jk; i recently made a water crossing that flooded the engine compartment and i know that the engine would not have survived if i had a k&n. i dont make many water crossings, but for me, its not worth the risk.

 

K&N is good for an increase in gas miliage in the JK. Performance you really won't feel.

 

A slightly better mileage makes sense, because you improve the air flow (2 MPG is really surprising if you think about it). The issue I've heard with K&N filters (or any oil based filters for that matter) is that they let more particulates past them.

I have no proof that this would be a problem, but I'd rather pay a slight mileage penalty then take a chance of wearing down the engine because of dirt getting past the filter.