Air Filters


My sons tell me that by replacing the stock air filter on my 2005 BMW X3 with a K&N air filter(or similar) I can increase my gas mileage by 3 to 5 miles per gallons.

Is it true? Do I have to worry about my engine sensors?

I seriously doubt that large of an increase is possible. We are talking 20-25% mgpg increase here. If it were that easy, every OEM manufacturer would be using them, for CAFE reasons.

Aaron Gold at thinks you can get a 1-2 mpg increase total by following ten of his suggestions. One of them is using a K&N filter. This figure is more believable than 3-5 mpg.

I have tried K&N filters before on some of my vehicles and never noticed any performance gains or fuel economy gains. I could not justify installing one based on my experiences. It is also easy to over-oil it while servicing it and contaminate your mass airflow sensor.

Your sons are very incorrect. If fuel mileage could be increased by even 1 MPG you can bet the car makers, with mandates by the Feds, would have done this on the assembly line when building the car.

Your gas mileage will not increase. You engine life may decrease.

BMW really wastes money when they pay all those engineers to design something for optimum performance. I wonder why BMW doesn’t just buy K&N filters. You should wonder too. A lot of people have sons or relatives that will say things for no real reason. It’s just life.

I’ve used K&N filters on several of my cars and trucks, never noticed any discernable increase or decrease in mpg.

Sensor damage may occur if the filter is over oiled after a cleaning.

Ed B.

Think about this for a second…

So the idea is that the air filter is restricting the airflow into the engine, causing the engine to work harder to pump the air through. But, if you’re at anything other than full wide-open throttle, what’s the biggest restriction? The throttle plate! So unless you’re talking about improving your economy while the pedal is to the floor, there’s not going to be any effect-- it’s basically the same as holding the throttle open a little bit more.

The only tangible effect of high flow filters on an otherwise stock car is that it will make the engine louder, which is why people report more power but also I think why they sometimes result in better fuel economy-- if you’re already driving with a mind to improve your economy, if you hear the engine roaring at lower RPM’s, you’ll probably tend to drive a little bit more conservatively.

Do I have to worry about my engine sensors?

Yes If you don’t oil the filter just right the filter will not be filtering out the dust and/or it can damage MAF.

Thanks for all your replys. I agree with you.