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Air filters

what are the signs that I may need a new air filter?

Visual inspection.


how would an old/dity air filter effect my vehicles performance?

Yes. But it would be so subtle you probably wouldn’t notice, unless contaminates got onto the MAF sensor. At that point the Check Engine light comes on. That’s why you remove it and check it out.


Thank you

What is the service interval recommended in your manual? It should be visually inspected at around half the service life. YOu can change an air filter too often. They let too much junk in when new because trapped material can increase the filtering efficiency.

Somebody wrote to us a while ago saying that he changes his air filter every 13,000 miles as recommended for his truck. At 15,000 miles, mine didn’t really have to be changed but it was ugly so I spent the fourteen dollars. It was a huge filter. If you drive through a Maine Winter dust and sand festival, I say that would be one sign of needing a filter. I made it through three Winters but I only drive 5,000 miles a year in that vehicle and there isn’t always somebody in front of me putting a ton of dust in the air.

I generally totally agree with Tester, but this time, only sorta.

While Tester can visually inspect a filter and make a good estimate, most owners, are not going to be able to tell just by looking. Yea, most owners can tell new from completely blocked, but there is a lot of in between.

I suggest that most owners can follow the recommendations in the owner's manual and they will not be far from right.  Of course if you just drove through a dust storm, likely you need it changed. 

I will go along with the Beads… as well. You can over do changes.

I will go so far as to suggest that as long as you are in the ballpark, you don’t need to be exact with changing air filters. I have never heard of a air filter related problem when using recommended filters and recommended filter change intervals listed in the owner’s manual

Avoid oil filters like K&N unless you want to live dangerously and like replacing MAFs.

I concur…The air-filter change recommendations in my manual say every 20k miles…I change about every 8k miles…and it’s close.

K&N filters get a bad rep due to people not knowing how to clean them properly. I have a K&N filter on my Mustang. When I was having it dyno tuned (an absolute must when you add forced induction) for shits and giggles I had them do a pull with a papaer filter I had handy which had been through about 7k-8k miles of use. The pull with the K&N filter netted an increase of 4 RWHP. The same tune was used for each pull. I have never had a problem that was related to K&N filters on any car I’ve ever owned. My Bronco has had the K&N for almost 120,000 miles. I clean it properly every other year or so and haven’t had any issues. The problem is people use too much oil when then clean them, the extra oil contacts the MAF sensor and it quickly burns out.

K&N filters get a bad rep due to people not knowing how to clean them properly.

True. But the fact remains that many people who have them don’t clean them properly. For most all drivers they are a bad idea. I might also suggest that I have seen test results indicating that they don’t filter as well as standard filters, but frankly I have not seen any evidence that the filtering issue has resulted in any problems.

It should be visually inspected at around half the service life.

That is not always a good idea. On some cars (including mine a 2002 VW TDI) the filter gasket is designed for a one time use and it will not always seal properly a second time.

I use the "hold up to light (or the sun) method. If you can see light through them, and the light is pretty good through most of the filter, then it’s ok. Now how much light should you see? That is where nothing but experience will help. Sufficient light for one person is not enough for another. I have always used this method, and have looked at probably a hundred of them, and feel like I’ve never changed a filter needlessly, and always changed them when needed. Course that is JMHO.

You must have produced near 400 HP with the power-adder unless it was a Mustang II. That is only 1% improvement with a used filter. The next question is, how reproducible are the runs and are they significantly different?

A lot depends on the environmental conditions. Here in OK it’s possible to install a new filter and then have to turn around and redo it 2 weeks later; especially during springtime and early summer when wheat harvest is going on.

There’s a huge grass fire about a 100 miles SSW of me right now and it’s been lightly raining ash here for about 5 hours. West of here it’s almost a snowstorm of ash and just imagine how much of that is being pulled into automobile intake tracts.

Yes, It put down 355 RWHP with the K&N, 351 with the paper filter. That translates in about 390ish-400 HP at the crank. In the interest of reliability and longevity, I opted for the conservative “safe” tune. I only run 6 pounds of boost. The runs were done within 10 minutes of each other, engine temp and air temp was about as close to the same as one would expect in a 5-10 minute span. The K&N pull was first, the paper filter was last, as it was kind of an afterthought. I’m told with a more aggressive tune 390 RWHP is attainable. But for a daily driver I can make due with 355.

On many vehicles it’s really easy to change the air filter, and any I’ve gotten were pretty cheap - so I just change it every year. Any used car I’ve ever purchased - the filters were really dirty or covered in straw or cat hair! The last vehicle I bought I swear they had never (7 years) changed it!.I put my shoulder out getting it out, and killed one of my socket wrenches (dodge caravan - harder to get at). Still glad I did it though.

Here in OK I even clean the condenser coil in my home central A/C unit about twice a year; once at the end of winter and generally about halfway through summer.

On a number of occassions I’ve found the condenser clogged pretty badly only a few months after cleaning it. When the blowing milkweed is bad it makes the situation even worse by collecting dust, wheat chaff, etc.

One can imagine what’s happening with auto air filters.

Maybe that is what they are supposed to look like when they are replaced. HDYK it is not filtering best when it is half-spent? YOu may be sucking lots of extra particulates into the engine by replacing the filter too soon.

IIRC, the wife’s vehicle calls for replacement every 30K. It is a 4-banger, but the filter element is bigger than the filter on my V8 car. A filter element is $25 at the dealer, but I just bought an OEM filter for $14 mail order.

Sounds like K&N could make a killing with a really big filter for home air conditioners.