I'm thinking about using K&N airfilters to perhaps eek out a bit more gas mileage on my '03 C240 4Matic wagon. Right now I get about 22mpg city/28mpg highway, which I consider fairly good.
Can anybody attest to an improvement of fuel economy through their use? If so, how much increase did you get? And...is such an increase worth the cost? (These filters cost around $40-50 each.)
Also...the K&N Website indicates that two (2) filters are required in the 2.6L V6 C240 engine. Is this so? Without taking the airfilter box apart, I'm curious to know how and where two filters would fit.
I've run both K&N and ITG airfilters on my C230 and did a mileage test on the same stretch of road at constant speed and there was no difference. K&N has in the past few years developed a reputation for having the oil vapors from the filter work their way to the MAF sensor wire. Of course K&N says no but many people on the forums, specially those with the V6 have complained of MAF errors after installing a K&N filter. Also, I've seen tests where the K&N filter doesn't filter as well, another reason for destroying the MAF sensor. In the old days of carburators it didn't matter, very small dust particals would just get burned up in the engine. This is way more critical with fuel injection systems and all the sensors.
With all that said, I had no ill effects from running either filter.
Vehicle: 1980 w123 230 "Sport", 2005 w203 230 Sport
Location: Outside of Buffalo,NY
Posts: 1,968
On my short runner VR6 Corrado I had the K&Ns coat the MAS...on my older MAP unit in my w123 there are no problems...
Check and maintain your tire pressure - or use inert gas - you will probably get better gas mileage...or only run around with a ½ tank of fuel or less…
Information & Advice Sought on K&N Airfilters 
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