K&N Million-Mile Air Filter Review

The Air Filter That Never Gets Thrown Away

Paper and K&N filters
Paper air filter on the left, K&N air filter on the right.

Photo: Aaron Gold

K&N makes drop-in replacement air filters which can be cleaned rather than replaced. K&N claims the re-useable air filter saves money and landfill waste, and that their filters are less prone to air restriction as they get dirty. (Restricted airflow causes a reduction in engine power and fuel economy.) Retail prices range from $35 to $80+ depending on the application.

How Does the K&N Filter Work?

Engines produce power by igniting a mixture of fuel and air. The air filter's job is to filter out particles of dirt while allowing a free flow of air so the engines can "breathe". A filter that is clogged with dirt will cause loss of power and fuel economy.

Most air filters use paper as their filter medium. Most cars require the filter to be checked or changed every 10,000 to 20,000 miles; when the filter is dirty it is thrown away and replaced.

How Is K&N Different?

K&N air filters use an oiled cotton filter medium. K&N claims that not only do their filters allow freer airflow when clean, but they can absorb dirt without getting as restricted as paper filters. When the filter gets dirty, you don't throw it away; you clean and re-oil it. K&N estimates the cleaning interval to be about 50,000 miles (longer for less dusty areas). The filter is serviced with a K&N cleaning kit ($9 to $12 retail ) which is good for 5 to 10 uses. K&N says their filter will last the lifetime of the vehicle and covers their filters with a 10 year/million mile warranty.

Benefits of the K&N Air Filter

Environmental Benefits

Paper air filters cannot be recycled; you have to throw the whole thing away. The K&N filter itself lasts the life of the car, and the cleaning kit uses cardboard packaging and plastic bottles which can be recycled.

Cost Benefits

Cost savings depend on the application. I tested the K&N filter on our 1996 Honda Accord. Retail price for the K&N filter is about $43. (My test sample was provided free of charge by K&N.) Paper filters range from $19 to $31. Honda recommends a filter change at 15,000 miles, so for a do-it-yourselfer like me, the K&N filter and a cleaning kit will pay for itself after two changes or about two years. For people who have their cars serviced by the dealership, installing a K&N can pay for itself in a single change.

Real-world Benefits

Here's the reality: I'm not nearly as careful as I should be about changing my cars' air filters. By the time I get around to it, the filter is usually clogged with dirt—and that means it's costing me more at the gas pump. The K&N's longer service interval means that I can gleefully ignore it without such adverse effects.

Other issues with the K&N filter

How Well Does It Filter?

Several readers have responded with concerns about the K&N's ability to effectively filter dirt out of the air compared to paper filters. After all, engine protection is the reason engines have an air filter, to begin with. K&N insists that their filters are rigorously tested to meet OEM filtration standards.

Expert Opinion: Not an Issue

We discussed the issue with the owner of a reputable engine rebuilding shop. In his experience, the engines that suffered from premature wear were those in which the filters were routinely ignored. He didn't see any significant difference in wear in engines where the filters were routinely cleaned or changed, regardless of type. (He personally runs K&N filters in his own cars.)

Will the K&N Increase Engine Power?

Many enthusiasts use K&N filters because their increased airflow boosts power, especially in certain applications. If you are replacing a clogged air filter, you will definitely see a difference. Also, K&N sells a special intake kit for Accord owners like us who want more power.


Advantages of the K&N Filter:

  • Easy installation—same as a paper air filter
  • One less maintenance task to worry about
  • Environmental advantages—less waste produced
  • The potential for better long-term fuel economy

Disadvantages of the K&N Filter:

  • High initial purchase price


A useful purchase for most car owners—even if the cost benefits aren’t huge, the benefit to the environment is significant.