When do you change your air filter?

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I have seen a lot of people here that seem to only change their oil filters every 20 years. I live in an extremely sandy environment here on the coast and change mine every other oil change. My Ram uses a flat, oiled P1 and my Escale uses a larger conical Purolator Classic, motocraft, Wix or whatever I can find (I try different brands depending on what is available. They are sometimes hard to find.). By the time I change them, they are black and full of dust. I don't have a filter minder, I just change them by sight.

I have heard some people change them based on filter minders and some that say they filter better when dirty (makes no sense to me). I don't have a filter minder on my truck yet (looking to install one soon) and can't install one on my escape due to the way the air box is designed.

How often do you guys change your air filters? Just wanted to get an idea of the general consensus here. The majority of people I talk to outside of here don't seem to think about their air filters, and they could be the most overlooked filter on vehicles today.
 
Originally Posted By: Olas
I change my air filter at six inches of water


Not sure I follow...

You don't change your air filter until you hit high water?
 
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Originally Posted By: jk_636
I have heard some people change them based on filter minders and some that say they filter better when dirty (makes no sense to me).


OK, you have pingpong balls and tennis balls floating down a river. (dust in air is the analogy). You install a net (filter) that lets pingpong balls through, but not tennis balls.

At first the net lets all the pingpong balls through, until some of the pores get clogged with tennis balls..then the tennis balls start catching pingpong balls and trapping them.

The net's efficiency at catching pingpong balls increases markedly as the net (filter) gets clogged.

Air filters to the same.

The pollution control fabric filters on power stations filter the "smoke" out of the flue gasses, and don't work really well until they are "blinded" by ash, needing to have only small amounts of gas trickled in until they can filter properly, then have at em.

The filter minder stops the filter from exceeding a differential pressure that could damage it (a blocked filter could get sucked in by engine vacuum).

And the best part is that as you drive at part throttle anyway, your mileage doesn't change as it clogs (unless you have a carb)
 
The owner's manual says to change my car's air filter every 50,000 miles and that seems to be about right. I went 72,000 on the last one and I found the car ran fine but it started to draw oil out of the fresh air breather into the intake/throttle body.
 
Originally Posted By: Shannow
Originally Posted By: jk_636
I have heard some people change them based on filter minders and some that say they filter better when dirty (makes no sense to me).


OK, you have pingpong balls and tennis balls floating down a river. (dust in air is the analogy). You install a net (filter) that lets pingpong balls through, but not tennis balls.

At first the net lets all the pingpong balls through, until some of the pores get clogged with tennis balls..then the tennis balls start catching pingpong balls and trapping them.

The net's efficiency at catching pingpong balls increases markedly as the net (filter) gets clogged.

Air filters to the same.

The pollution control fabric filters on power stations filter the "smoke" out of the flue gasses, and don't work really well until they are "blinded" by ash, needing to have only small amounts of gas trickled in until they can filter properly, then have at em.

The filter minder stops the filter from exceeding a differential pressure that could damage it (a blocked filter could get sucked in by engine vacuum).

And the best part is that as you drive at part throttle anyway, your mileage doesn't change as it clogs (unless you have a carb)


Thanks for the breakdown. I understand the analogy, but still question air filter "loading".

What sizes are we talking about? What size particulates (in microns) will be caught with a fresh filter and what sizes won't be caught until it is "loaded? For example, Purolator says the Pureone oiled air filter is 99.5% efficient, but doesn't quantify that like they do in their oil filters.

I have heard people say that KN filters aren't efficient at all. What size particles do they fail to trap, and wouldn't filter "loading" apply to them as well?

Originally Posted By: WobblyElvis
The owner's manual says to change my car's air filter every 50,000 miles and that seems to be about right. I went 72,000 on the last one and I found the car ran fine but it started to draw oil out of the fresh air breather into the intake/throttle body.


I know that these answers will definitely vary. Those who live in cleaner environments (less dust and air pollution) should be able to go farther. I think there is most likely a lot less air pollution in Canada then on the beach 1000 yards from my front door lol.

Thanks for the input thus far guys!
 
Originally Posted By: mattwithcats
Every 15,000 miles...


This is about where I'm at. I change the air filter every other oil change in my wife's escape which is about 14-16k (7-8k mile OCIs) depending on how often I change it. My truck is closer to 10k after two 5k mile OCIs.
 
The Focus has a "life time" filter with a restriction gauge, so I hope I never change it. The other cars get one every 30-40k miles. None of them ever look like they are causing restriction as you can see that only one part of the filter is dirty.
 
Originally Posted By: IndyIan
The Focus has a "life time" filter with a restriction gauge, so I hope I never change it. The other cars get one every 30-40k miles. None of them ever look like they are causing restriction as you can see that only one part of the filter is dirty.


Man I feel sorry for you. My mother in law has a focus of that era and one of those "lifetime air filters" with a filter minder. Have you ever looked inside one of those? The ones I have seen have a baffle system that is open and for all intensive purposes empty. It doesn't filter for sh*t. Maybe the ones in the Canadian market were different than the U.S. ones, but here is an 04 I believe and it desperately needs an air filter.

It was a terrible system and was never designed to last. I spoke to a mechanic who told me that the focuses of that era were never designed to last more than 5 years and that when people trade them in full of problems, ford doesn't even bother fixing them or take them to auction. They just crush them and sell them to annhueser-Busch to make beer cans.
 
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Anyone install one of these?

threaded_mount.png
 
Originally Posted By: jk_636
Thanks for the breakdown. I understand the analogy, but still question air filter "loading".

What sizes are we talking about? What size particulates (in microns) will be caught with a fresh filter and what sizes won't be caught until it is "loaded? For example, Purolator says the Pureone oiled air filter is 99.5% efficient, but doesn't quantify that like they do in their oil filters.


Your premise was not getting why a filter got more efficient as it collected stuff, now you want particle by particle dissection...across brands ?
 
Originally Posted By: Ducked
IIRC the guideline is a vacuum excess (over a new filter) of 10 inches of water, so the six inches above is conservative. Nothing wrong with that, of course.

http://www.fueleconomy.gov/feg/pdfs/Air_Filter_Effects_02_26_2009.pdf



Here's a copy and paste from that pdf (sec. 2.3, last part of paragraph 2). The last sentence is an eye-opener
shocked.gif


"It is common, however, for servicing to occur when the filter appears dirty. Engine air filters are designed to actually increase their efficiency by using this initial layer of dust as an added filter layer. Initial filter efficiency is usually approximately 98% but increases to more than 99% by the end of the service life of the filter.7,8. Therefore, changing an air filter before the useful service life is achieved can result in premature engine wear.6,9."


According to my service log, I'm supposed to change my air filter every 30k miles.
 
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Originally Posted By: Eosyn
Originally Posted By: Ducked
IIRC the guideline is a vacuum excess (over a new filter) of 10 inches of water, so the six inches above is conservative. Nothing wrong with that, of course.

http://www.fueleconomy.gov/feg/pdfs/Air_Filter_Effects_02_26_2009.pdf



Here's a copy and paste from that pdf (sec. 2.3, last part of paragraph 2). The last sentence is an eye-opener
shocked.gif


"It is common, however, for servicing to occur when the filter appears dirty. Engine air filters are designed to actually increase their efficiency by using this initial layer of dust as an added filter layer. Initial filter efficiency is usually approximately 98% but increases to more than 99% by the end of the service life of the filter.7,8. Therefore, changing an air filter before the useful service life is achieved can result in premature engine wear.6,9."


According to my service log, I'm supposed to change my air filter every 30k miles.


Wow. That is an eye opener.

It seems the trick is figuring out when is the sweet spot and when it is over. That time where the filter is dirty enough to add additional filtration ability but not restrict airflow.
 
Depends, I guess.

The Bonneville has a K&N style cone filter that was already dirty when I bought the car over 50k miles ago. I haven't changed it or cleaned it.. it's absolutely filthy. The last UOA said air filtration was great, so I'm not touching it yet.

I will go by the owners manual on the Sonic for warranty's sake, witch I believe is 42k miles... I'll have to double check that. I just know we're not quite there yet. When the warranty is up, I'll install a restriction gauge.

I just put a new Wix in the Montana and it'll probably be the last air filter replacement it will get.
 
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