Can changing the engine air filte make such a difference?

[Flycaster]

My 2005 Z4 2.5i has 25K miles. According to the OBC, lately I've been getting about 20 mpg in mostly city type driving. This is a drop in mph from around 22-23 mph. I just replaced the the filter with an OEM Mann filter and the mpg has gone up to 24-25 mph. Is this possible, or am I dreaming?

[BruceJ]

Not to be crititcal, but kinda think it might have been more you being aware of the new filter and driving inadvertantly easier. If you really want to get scientific you need a measuring device/equipment that will ultimately allow you to calculate SCFM air flow of each. whichever one flows the most air will give you a little better milage, all other things being the same. Could be done, but time, money, expertise, etc. A better test might be to get it on a stretch of Highway, with new and old filters, under CC. Same conditions, same test.

Personally, I've never sweated city mpg's. Its hyper-dependant on traffic volume, route, traffic lights, etc. Just cant shine mpg consistently in the city. But its not a Prius, and hopefully thats why you bought it. Put the top down, shades on, and roll with it.

[ZStig]

depends on how long you've been keeping track of your mileage. If you measure it yourself not using the OBC, do a few weeks for a more accurate number

[WestCDA]

To answer your original question - yes, it's possible. Depending on how dirty the filter was that you replaced, it can have a significant effect on both engine performance and fuel economy.

[Flycaster]

Originally Posted by WestCDA

To answer your original question - yes, it's possible. Depending on how dirty the filter was that you replaced, it can have a significant effect on both engine performance and fuel economy.

Yeah, that's what I was thinking... Also, although the OBC is not the most accurate way to measure these things, if my mpg stays in the 24 mpg range, I'll still have a pretty good idea that the new filter did the trick. BTW, my driving manner hasn't changed since the filter went in.

[Drezahl]

it is entirely possible to notice better mileage with the clean filter. I notice the same type of thing right after I have new plugs installed - maybe a better more efficient spark that ignites more fully and eliminates wasted fuel.

I think those are certainly possible. Although I sometimes feel like the car is faster after a very good wash and wax - less drag?

[AirOpsMgr]

I constantly tested my mpg after switching from a used/slightly dirty OEM filter to a K&N high-flow filter and did see a gain of 4-5 mpgs (At sustained freeway speeds, allways using same fuel).

[fercho]

I just install the afe intake on my car and I am getting like 2 more mpgs

[Flycaster]

Not to burst any bubbles, but I have read that the K/N filters really don't do anything to boost HP; although, mpg may get better. And, BTW, remember that i use a relatively cheap Mann OEM filter...nothing fancy.

[Shipkiller]

Originally Posted by Flycaster

Not to burst any bubbles, but I have read that the K/N filters really don't do anything to boost HP; although, mpg may get better. And, BTW, remember that i use a relatively cheap Mann OEM filter...nothing fancy.

Read this:

http://www.shipkiller.com/AirFilters.html

I just put a Mahle (also OEM) in the ///M this weekend. AdvanceAuto has them cheaper than the dealer. I change my filter every 10K miles.

[santov]

I change mine every 10k or so, but I also take it out and use the shop vac to vacuum the dirty side of the out. I usually get lots of lint and leaf particles. Then I use the air gun (on stun not kill) to spray from the clean side down. Lastly I use the shop vac crevice tool to vacuum out the sand and crap that's collected at the bottom of the airbox.

I've tracked every single fill-up since I bought the car with aCar for Android:
Average MPG is 26.726 with a max of 30.772. Using Sport mode or lots of stop and go traffic I'll have a tank of around 24MPG.

I just got new non-runflat tires, so we'll see how MPG changes.

[Pheonix]

Originally Posted by fercho

I just install the afe intake on my car and I am getting like 2 more mpgs

The opposite happened after i installed the AFe on my car! But it mainly because i stay on the lower gear longer just to hear the engine roars

[fercho]

hahaha yea that's what I noticed I am spending more money on gas just because i want to hear the filter hhaha

[Uncle Russ]

I'm considering getting a couple of K&N air filters so I always have a clean one ready. The best mpg I've seen since I bought my ///M this past summer was 29 on the interstate. Now during my weekly commutes in NoVA, it's down to 21.8. I'm hoping the Inspection 1 it's going under right now will bring it back to 24. Still pretty darn good for a hi-performance I6!

[kj.marway]

Hi all,


I've just joined the forum (not trying to hijack the thread at all!) so thought I'd say 'hi' and add to this thread. I bought my 2.5i Z4 Roadster (2007) from BMW Park Lane here in London - for those outside of the UK, this is the only dealership (to my knowledge) that is owned directly by BMW UK, and not a franchise.

Anyhow, when I checked my air filter, it seemed a little worse for wear and so after much deliberation over a K&N filter, I went for a Mahle LX-1250 filter. Having fitted the part, all seems well and if anything, the Z feels sharper in throttle response and sounds as though its 'asthma' has been cured.

Disappointingly, it seems the air filter wasn't changed prior to buying the car (I've attached a comparison photo at; http://goo.gl/HxoGBZ ) - any advice as to anything else they may have skimped on?



Many thanks in advance!

[jdoublehcubed]

Originally Posted by Flycaster

My 2005 Z4 2.5i has 25K miles. According to the OBC, lately I've been getting about 20 mpg in mostly city type driving. This is a drop in mph from around 22-23 mph. I just replaced the the filter with an OEM Mann filter and the mpg has gone up to 24-25 mph. Is this possible, or am I dreaming?

That sounds crazy low for a 2.5i. I get around 19.5 in my M (all around average). Thats a mix between city and ~85mph on the highway, and driving the car with a lead foot pretty much all the time. I don't understand how you could get a 2.5i down to that mileage, even it it was 100% city driving. I would try cleaning the MAF sensor as well and seeing if you pick up another 2-3 mpg.