Air filters


I was wondering if anyone has used after market air filters, like K&N, and what you think about them? I have a 2006 Chevy PU and use e85 fuel. I am more interested in increasing my fuel mileage than any performance.


The problem with K&N filters are the constant maintenance. The filters last for a million miles (supposedly), but need to be cleaned and oiled to work. Also, if your truck uses a hot-wire-style MAF sensor, over-oiling the filter can lead to damage to the MAF sensor. The OEM-style paper filters are non-maintenance, and just require regular replacement.

As far as fuel mileage savings, all that work may save you up to 1/2 MPG. A freer flowing exhaust may add another 1/2 mpg. But, it also depends on how you drive.


They’re NOT worth it. To make a vehicle breath more (which they claim) then it MUST be filtering LESS. Engineers for the manufacture have designed a happy medium of filtering and air-flow. Stick with a standard air-filter and you’ll be far better off.


If you really want to improve your mileage, use regular gasoline. Ethanol has less energy, so you get less bang for the buck.


The stock filter in your truck is huge. You won’t get better mileage with another type.


I have a K&N in my Ranger, and I think it works great. Can’t tell for sure if it adds power and/or mileage, but what does a paper filter cost, 7-10 bucks? The K&N I bought was about $30, so technically I’ve broke even by 60,000 miles. And constant maintenance! What do you call changin’ the oil? Caring for you K&N is rather simple: when it gets dirty (and technically the dirt acts as a filter), usually around 15,000 miles, take it out, gently hose the filter out, let dry, and lightly re-oil.


Back in the days of hotrods helping an engine breath better could make a big improvement in mileage and power. Today’s cars are far better in that line and don’t really need any help unless they are modifided. Many modern cars have sensitive sensors to measure the air comming into the car. K&N filters use an oil charge to work. You need to clean and recharge the filter as part of it’s maintenance and if you get a little too much oil or don’t get it evenly oiled you can damage that sensor or allow a lot of dirt into your engine.

Under ideal conditions you could gain a very very small improvement in mileage. The numbers most users report are mostly placebo effect. If you drive a little more carefully you can gain far more mileage.


i was wondering. why do you use E 85 (85% ethanol) fuel? why don’t you use regular (10% ethanol) added gasoline?

that has WAY more to do with MPG than the air filter.


Most people over oil the K&N and over time this coats the airflow sensor reducing mileage. I get over 100K on a paper filter so it would never pay me back.


I get over 100K on a paper filter so it would never pay me back.

100k…WOW…I’m lucky if I get 20k miles.


The value of K&N filters has recently been touted as an ecological alternative to disposable paper filters, which are made from trees and end up occupying landfill space. Personally, I think this is just a marketing ploy. My take on this is that in order to take advantage of the increased performance they provide by helping your car breathe easier, you would really need to modify other aspects of the car, like the exhaust system. While this might increase horsepower, it will only lead to lower fuel economy. Even if the K&N filter alone helps your truck breathe easier, your engine will need to use more fuel to maintain the proper air/fuel mixture, which will lower your fuel economy.

For the best fuel economy, stick with your stock equipment. Aftermarket parts are made for increased horsepower and performance, which will only end up using more fuel.

Regarding the argument that they will harm your engine, this is just an assumption based on faulty logic. They allow the engine to breathe easier not by filtering less, but by simply increasing the surface area of the filter. So if you decide to upgrade, don?t let fear and faulty logic keep you from doing it. Just don?t expect an increase in fuel economy.

Lastly, when you use E85, you should expect lower fuel economy per gallon. That is just how E85 works. In order for E85 to be cost effective, it really needs to be priced a lot lower than gasoline. If they are priced around the same amount, you might be better off buying gasoline.


I learned this here on Car Talk. Go to and read the air filtering test article. Regular paper cartridges filter the best.


That is an interesting test, but there are a couple things that I would have liked to have seen:

  1. The K&N filter tested is one that fits into the stock housing. I am not at all suprised to see a filter that fits into the same space with increased airflow filter less effectively. Yes, airflow and filtering, with all other things being equal, have an inverse relationship. The K&N filter that I was thinking of is the round one that requires a modified air intake like the one at

  2. I would like to see a study that includes other brands of paper filters like Fram and Purolater.

So, djdavisson, if you are looking into using a K&N filter that fits into the stock air filter housing, yes, you should expect it to filter less. However, that isn’t necessarily true for a modified air intake system. However, like I said, modifying your air intake system will likely reduce your fuel efficiency.


Thanks for the input! I am able to buy E-85 fuel at $2.10 per gallon so it is worth the reduced fuel economy. I would like to increase my milage and that is why I have been looking at the fitlers. I get about 14 mpg on the road and at a speed of about 60 but if I take it up to 75, the milage really drops, down to about 12 mpg. Thanks again. djdavisson


As you likely know E-85 has less energy per gallon so it is going to give lower mpg. As you increase your speed it is starting to run at a higher duty cycle and that is likely to decrease overall efficiency so you will have two factors against you.