Should you ever change your air filter?

[KrisZ]

My last air filter went about 60k miles and still showed no restriction on the gauge. I changed it because the seals were cracking at the corners, probably because I opened the box few times. This time I will just let it ride without touching the filter.

 

[Errtt]

Jim... I re-read this post/replies and I don't know what to say except this is a very educational reading. I've never put much thought regards to air filters.
All I can say is thank you Jim, I'm soaking the information and will now have a different perspective on filters, air filters.
Now the filter grease mentioned. I never knew, and now I want it. Going on the search for it. I'm leaving my filter alone until at least I have some. Then will grease up a new filter on install when ready to change filter. Also, I have to get a filter indicator now, must have (sometime "I want" means must have if you know what I mean).
I guess the only filter I'll clean now is the K&N on the Harley because that's all I have for it, for now. At least it was only getting checked about every 2 years, and last check I didn't clean & re-oiled it because it still looked fine to me. But when I do remove it, I try to look into the carb throat to see how clean/dirty it looks. Now I'll look more carefully/harder with good lighting.

 

[rrounds]

Here's the one I use on my truck and Honda S2000, have over 60k miles on the S2000 filter and still no restriction.
http://www.summitracing.com/parts/wix-24801/overview/

ROD

 

[gaijinnv]

Originally Posted By: rrounds
Here's the one I use on my truck and Honda S2000, have over 60k miles on the S2000 filter and still no restriction.
http://www.summitracing.com/parts/wix-24801/overview/

ROD


Unplug that one and plug in this one:

The K&N is much more sensitive and more suitable for gasoline engines.

 

[Jim Allen]

One thing I'll add is that the K&N gauge is calibrated (as you can see in gaijunnv's pic) to go "red" at 10 inches of water. That is the spec K&N uses for their filters because they are low restriction and high DP tends to start pulling dirt thru. If you have an ordinary cellulose filter, you want to use 15" as a the "red" spec because they have inherently higher DP (differential pressure) and don't flow quite as well. If you used a 10" filter with paper, it might trip too early. A 10" gauge might be a good idea for the performance oriented driver who wants his WOT power at 100% at all times, but you can buy gauges that will trip red at 15" but will indicate actual restriction and then all you have to do is service at 10".

General things to keep in mind RE restriction gauges:

-They come with different settings for different applications and you want the right one for your engine.

-Some engines will have higher initial readings with a new filter than others. That's why you get your baseline with a new filter and go out to "set" the gauge with a couple of WOT runs to rated max revs. Some cars will barely move the gauge, others will show a reading and some will be higher than others due to inherent intake restriction (which could be the plumbing as much as the filter). That is n't necessarily anything to sweat, especially if you are not performance oriented, and rest assured the engine designers know about it and it's factored into their design.

-For fuel injected gas engines, you generally want one that goes red at 15" of water (about 3.7 kPa).

-For light duty diesel engines, you want a gauge that goes red at about 25" of water (6.2 kPa). Some HD engines go to 30 " (7.4 kPa).

-Get on that has a scale so you can follow the restriction as it increases. Try to get one that has as many graduations below your max number as possible and with as low a lower number as possible. This is more for informational purposes than anything... it isn't strictly necessary, it just is geeky fun to track it.

-Restriction under 15" doesn't decrease fuel economy in an EFI engine, but I have been told by experts that if you are an economy minded diesel owner, air filter service at 20" can result in slight to moderate fuel economy gains. Diesels are more sensitive to restriction, moreso older mechanically injected diesels.

-I have been told that restriction gauges on carbureted gas engines do not provide reliable readings but I have some cause to doubt that... but I won't go into it now. trying to get it lined out. I have a gauge on a carbureted engine that came with one from the factory (a gasoline powered John Deere combine).

 

[gaijinnv]

Originally Posted By: Jim Allen
One thing I'll add is that the K&N gauge is calibrated (as you can see in gaijunnv's pic) to go "red" at 10 inches of water. That is the spec K&N uses for their filters because they are low restriction and high DP tends to start pulling dirt thru. If you have an ordinary cellulose filter, you want to use 15" as a the "red" spec because they have inherently higher DP (differential pressure) and don't flow quite as well. If you used a 10" filter with paper, it might trip too early. A 10" gauge might be a good idea for the performance oriented driver who wants his WOT power at 100% at all times, but you can buy gauges that will trip red at 15" but will indicate actual restriction and then all you have to do is service at 10".

General things to keep in mind RE restriction gauges:

-They come with different settings for different applications and you want the right one for your engine.

-Some engines will have higher initial readings with a new filter than others. That's why you get your baseline with a new filter and go out to "set" the gauge with a couple of WOT runs to rated max revs. Some cars will barely move the gauge, others will show a reading and some will be higher than others due to inherent intake restriction (which could be the plumbing as much as the filter). That is n't necessarily anything to sweat, especially if you are not performance oriented, and rest assured the engine designers know about it and it's factored into their design.

-For fuel injected gas engines, you generally want one that goes red at 15" of water (about 3.7 kPa).

-For light duty diesel engines, you want a gauge that goes red at about 25" of water (6.2 kPa). Some HD engines go to 30 " (7.4 kPa).

-Get on that has a scale so you can follow the restriction as it increases. Try to get one that has as many graduations below your max number as possible and with as low a lower number as possible. This is more for informational purposes than anything... it isn't strictly necessary, it just is geeky fun to track it.

-Restriction under 15" doesn't decrease fuel economy in an EFI engine, but I have been told by experts that if you are an economy minded diesel owner, air filter service at 20" can result in slight to moderate fuel economy gains. Diesels are more sensitive to restriction, moreso older mechanically injected diesels.

-I have been told that restriction gauges on carbureted gas engines do not provide reliable readings but I have some cause to doubt that... but I won't go into it now. trying to get it lined out. I have a gauge on a carbureted engine that came with one from the factory (a gasoline powered John Deere combine).


All good points, Jim.

I originally had the Wix gauge rrounds cited in his post. It has a maximum reading of 25" H2O. When I did my WOT runs to establish a baseline, it still indicated no restriction.

When I substituted the K&N gauge which has a maximum reading of only 10" H2O, however, after my WOT runs it indicated a restriction of a little less than 50% (5" H2O).

Chalk me up firmly on the "geeky fun" side of this one. I am looking forward to noticing the first indication of restrriction on my gauge, and I know I'll see it a lot sooner with the K&N gauge than the Wix gauge.

Since I still have the Wix gauge, I could always plug in the Wix gauge after the K&N gauge indicates 10" H20 so I could watch it climb to 15" H20.

Or ... I could install BOTH gauges on my filter box so I could watch their indications increase sequentially

Now that would be geeky fun

 

[Jim Allen]

You bring up a good point that I should have elaborated more on. Some engines simply have very low restriction intake systems from the factory. Others are high from the factory. You'll find out the first time you do the WOT test, so the restriction gauge could be useful as a tuning tool as well. Typically the gauges stay at the initial restriction for a good long while and rise slowly as the filter loads but it's usually on an rising curve. One day you well see little restriction and a two months later you note a sudden rise that will soon pop into the red.

The 25" gauges often don't even start until 8 or 10" whereas a 15 or 20 inch guage might start as low as 5". For geeky fun, of course.

 

[rrounds]

My Wix starts at 8" and I'll change the filter long before it gets to the red, somewhere around 15". My Wix gauge has stops at 8", 11", 15", 22" and goes to red at 25" so I have stops both below and above where I'm going to change the air filter.

The Honda S2000 has a cone filter inside of a box that you can take the lid off of and still filter 100% of the air(some take the top off to hear the intake-it's very loud with the lid off).

With a new air filter my S2000 will read 8" with the top on but not read any restriction with the top off, what that tells me is Honda made the air opening for the air box to small. I and other S2000 owners would not know this without the restriction gauge.

ROD
p.s. I still don't get to the 8" mark with the top off even with 60k + miles on it

 

[AKhan87]

Originally Posted By: Jim Allen
I guess I have to explain further.

For every one like you, cheespuff, there are 10 reading this exchange who are in complete ignorance of the topic and have no idea of the science behind it. Is it better to teach them the whole shebang properly or just say, "don't worry about it?" If you have the knowledge then you can evaluate your own situation and make the right choices. Everything I said is factual and based on sound automotive science.

I also think you are missing another point. I am not advocating longer filter intervals just so it will get dirty and be more efficient. I am trying to help people not obsess over a slightly dirty air filter and change it too often, unnecessarily. Especially for some unquantifiable and unmeasurable non-goal as "responsiveness." Or thinking it's somehow "better" or "beneficial" for their car to do so. Clearly it is NOT beneficial to change the filter more often than necessary and it's a waste of money. All I am doing here is giving people a metric for the RIGHT time to change the filter.

I don't lose sleep over people changing their filters too often but I am often gobsmacked over people who argue in favor of wasteful and counter-productive maintenance practices.



Well i really appreciate it Jim. Running my air filter longer is not only cost effective it is also environmentally friendly while giving the engine extra protection!

 

[Jim Allen]

Originally Posted By: rrounds
My Wix starts at 8" and I'll change the filter long before it gets to the red, somewhere around 15". My Wix gauge has stops at 8", 11", 15", 22" and goes to red at 25" so I have stops both below and above where I'm going to change the air filter.

The Honda S2000 has a cone filter inside of a box that you can take the lid off of and still filter 100% of the air(some take the top off to hear the intake-it's very loud with the lid off).

With a new air filter my S2000 will read 8" with the top on but not read any restriction with the top off, what that tells me is Honda made the air opening for the air box to small. I and other S2000 owners would not know this without the restriction gauge.

ROD
p.s. I still don't get to the 8" mark with the top off even with 60k + miles on it


Knowledge is power, Rod; you're doing it right! Another good example of how to use a restriction gauge.

 

[nickolas84]

Originally Posted By: Jim Allen
... high DP tends to start pulling dirt thru.

I guess there is an element of time, typical testing do not account for.
Is it different to load up a filter in few hours or minutes to loading up over thousand of hours in opperation?
I mean regular testing indicates that a filter only clogs up as time passes and DP increases. Are there tests that prove that prolonged average to high DP (let's say from 10'' all the way to 25'') doesn't damage the filtering media in a way that allows dirt to pull through?

 

[Jim Allen]

Originally Posted By: nickolas84
Originally Posted By: Jim Allen
... high DP tends to start pulling dirt thru.

I guess there is an element of time, typical testing do not account for.
Is it different to load up a filter in few hours or minutes to loading up over thousand of hours in opperation?
I mean regular testing indicates that a filter only clogs up as time passes and DP increases. Are there tests that prove that prolonged average to high DP (let's say from 10'' all the way to 25'') doesn't damage the filtering media in a way that allows dirt to pull through?


Good question.

It's essentially the same, though long term over-the-limit DP likely has a worse effect than short term exposure. It only stands to reason.

If you are staying within the design limits, the answer is no, IMO. I haven't seen any tests exactly like you wonder about but but design limits are design limits, safety factors are safety factors, and if the manufacturer rates the filter for a certain DP, then one assumes they have done the proper testing. A 15" DP is generally accepted industry-wide number for gassers, though there could be variations. In the cases where I have read about pull-thru, it was in extreme cases with very high DP. A certain amount of durability is built into the filters as a safety factor. Wouldn't it be great to know exactly what that is in each case?

 

[Shannow]

If I can add my 2c worth, and didn't think of the relevance until this part of the thread.

Another part of my career over the last 20 years has been Power station fabric filters...the filter media that filter the "smoke" out of the hot power station exhaust gasses...

Those around here run to 2.5kPa, which doesn't do them a great deal of harm, nor lead to excessive blinding...however, at high DPs, the mechanical aspects come into play. Every pressure cycle generates media movement.

Loosely fitted or poorly supported media fails very early.

Similarly, a poorly manufactured/supported air cleaner won't handle the fluctuations in airflow (think gear changes) over an extended period of time.

 

[Errtt]

Well I dropped a filter indicator in my Amazon cart for when I ready to pull the trigger - have other items to work on to go into the cart also.
Although I got into my filter today although I don't have the indicator yet. Then I found dual air filters (new post) huh!

 

[qnyla]

I wonder how often I should be changing my air filter in these conditions?

 

[gaijinnv]

Looks can be deceiving:

Just go by what the restriction gauge tells you

 

[Jim Allen]

Yet more graphic examples! I'm inclined to ask people to take pics of their used filters and their restriction gauges to show that dirty looking doesn't necessarily equate to high restriction.

 

[nickolas84]

Originally Posted By: Jim Allen
Originally Posted By: nickolas84
Originally Posted By: Jim Allen
... high DP tends to start pulling dirt thru.

I guess there is an element of time, typical testing do not account for.
Is it different to load up a filter in few hours or minutes to loading up over thousand of hours in opperation?
I mean regular testing indicates that a filter only clogs up as time passes and DP increases. Are there tests that prove that prolonged average to high DP (let's say from 10'' all the way to 25'') doesn't damage the filtering media in a way that allows dirt to pull through?

Good question.

It's essentially the same, though long term over-the-limit DP likely has a worse effect than short term exposure. It only stands to reason.

If you are staying within the design limits, the answer is no, IMO. I haven't seen any tests exactly like you wonder about but but design limits are design limits, safety factors are safety factors, and if the manufacturer rates the filter for a certain DP, then one assumes they have done the proper testing. A 15" DP is generally accepted industry-wide number for gassers, though there could be variations. In the cases where I have read about pull-thru, it was in extreme cases with very high DP. A certain amount of durability is built into the filters as a safety factor. Wouldn't it be great to know exactly what that is in each case?


Somehow I fear manufacturers haven't done this testing. It could be as simple as filter testing used filters like the one mentioned in your article. That would be anecdotal evidence but good enough for me!

 

[Jim Allen]

Originally Posted By: nickolas84


Somehow I fear manufacturers haven't done this testing. It could be as simple as filter testing used filters like the one mentioned in your article. That would be anecdotal evidence but good enough for me!


I know from being told by industry people that QC testing of all types is done regularly. But you have to realize that there is a lot of established engineering practice out there. They know a lot about filter design and that reduces the amount ot testing that needs to be done. In many cases, the media is rated by the manufacturer to the company that actually builds the filters to meet certain engineering specifications... including efficiency and structural (often the media comes from outside sources). No doubt there are spot checks but there is enough established engineering practice with air filters that many (if not most) design issues are known and accounted for by standard practice. It might be known, for example, that X media design built in Y fashion takes 30" H2O to collapse or start pulling dirt thru. They rate the FCI DP at 15" and determine that occurs at or past the normal vehicle manufacturer's recommended FCI so there is a lot of safety factor built in. The parameters might be checked occasionally. Nobody can account for el-cheapo companies putting out substandard products or neglectful owners who just never bother to service their cars.

 

[Vikas]

Jim,

Without a restriction gauge, is there some engine parameter that you can look to deduce that filter needs replacing? This assumes that we do not know the manufacturer specified maximum flow rate. All we know is the size of the engine and whether it uses MAP sensor or MAF sensor.

Thanks