As I rolled my 2-year-old Coupe over to 50K miles, it's time for maintenance work again. Checking with my local SF) MINI dealer, they checked the key fob and say I need "only" an oil change--and an engine air filter. ($400 for just that, to boot.)

I asked about switching to a K&N filter, having heard about their alleged benefits before but never having pulled the trigger. The reply was they were OK, but to avoid the "oil-based" one, as that oil could get into something that would cause problems (I forget exactly what she said). She also said it's likely increase performance--but decrease gas mileage.

Me, I'd rather "upgrade" if I can eke out an extra mile or two per gallon. I already found my mileage dipping a bit after changing out 2 tires to highly rated low rolling resistance ones, so I don't want to find my MINI trending down further toward 30 MPG; I'd rather find ways to push it toward the 40 mark (it'd been getting around 38 for the first year and a half I owned it).

So what does the hive mind say about K&N?

 

unless your filters really bad i'll be surprised if you pick up anything significant, unless you subconsciously drive it that way.

i think most of k&n's filters are oiled though, and not the best "filtering" - i'd just go with oem or check if amsoil's got anything that fits

 

Wait, what? $400 for an air filter? Or for that, and an oil change? WOW. Both are pretty easy DIY projects; the air filter doesn't even require getting under the car, and a good Mahle air filter is about $14 or so.

You can google "air filter myth lose mpg dirty" and get a bunch of hits, but the general theme is that modern engine control systems manage the air fuel ratio such that your fuel economy shouldn't be affected by a dirty air filter. A really clogged one might reduce overall *power* some, but it would still be running as cleanly as the system can manage.

Back in the [carbureted] day, a clogged filter *would* cause a richer mixture, much like having the choke on all the time, thus adversely affecting MPG. No chokes, or carburetors using them, these days.

 

A new K&N or an oiled foam air filter are oiled just right at the factory. The problem with oiled air filters comes when they are cleaned and re-oiled. Some people put too much oil on them and droplets of oil get on the mass air flow sensor causing it to malfunction and cause runnability problems.

Dave