Should you ever change your air filter?

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I am refering to stock type "paper" filters. It is common knowledge that the dirtier it becomes, the better it filters. Naturally at some point it gets clogged, but this is not as bad as you think. Fuel economy reduction is insignificant* with a moderate measurable reduction in engine performance according to this sae paper and this fueleconomy.gov paper

Should we ever change our stock air filter unless there is a reduction in power?

edit *modern engines
 
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if its closed loop with an o2 then you could probably run it for longer than you could run it in a carb'd motor, reading the MAF data in real time would be a good place to start, or a filter restriction gauge..

I've seen very old, very plugged up air filters that have started to cave in and collapse under vacuum so you can't leave them for too long, but upto a point, filtration improves with age.

Like most things, its a balancing act which is made easier when you have some data.
 
I get exactly where you are coming from...and agree to a point

We had fires here a few months ago, and weeks of smokey air. The filter on the Caprice looked worse than anything that I've ever seen, so I changed it.

When I get time, I'll look at the Nissan, and probably wash it (washable and oilable)
 
Take this one step further, and don't even check it. Invariably there are little leaks in the rubber seal, but they might fill up with dust and cure themselves. If you disturb the rubber seal, particularly taking the plastic airbox apart and reassembling it slightly differently, you can leak dusty air around it.

Restriction gauges are the way to go.
 
Originally Posted By: eljefino
.Restriction gauges are the way to go.


I looked into these a few months ago.., specifically for the 05 Accord.

is it common to have to drill an opening in the post air filter housing? Does it matter where this is/would be positioned? Top mount vs side... Or simply best fit?
 
It is true that most of these air filters last much longer than we imagine, but really if one drives alot it makes sense to grab a reuseble one. Alot of them offer better filteration from day one because of the oil material.

Ppaper is simple tho , small pebbles can damage these materials and boom there goes your filter media. thats why routine inspection ( with OCI ) and cleaning of the big derby is key.

I was able to find an AFe resueble, washble filter for 16 dollars on amazon , thats only a few bucks more than the paper stuff. rare case but it happens if your deal hunting often.all it takes is once a week check of prices , amazon already filters out stuff that is incompatible.

Modern engines dont run too rich or lean because of a filter, air fuel mixture is always set based on input air so with even very clogged filter MPG isnt hit too hard, acceleration is, i wont be having that.
 
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Originally Posted By: Finz
Originally Posted By: eljefino
.Restriction gauges are the way to go.


I looked into these a few months ago.., specifically for the 05 Accord.

is it common to have to drill an opening in the post air filter housing? Does it matter where this is/would be positioned? Top mount vs side... Or simply best fit?


My Cummins diesel came with one. They suggest not to open up the housing to take a look. Go by the gauge.
 
Originally Posted By: Finz
Originally Posted By: eljefino
.Restriction gauges are the way to go.


I looked into these a few months ago.., specifically for the 05 Accord.

is it common to have to drill an opening in the post air filter housing? Does it matter where this is/would be positioned? Top mount vs side... Or simply best fit?


Good question. Wish they were integrated as oe.
 
Originally Posted By: JHZR2
Originally Posted By: Finz
Originally Posted By: eljefino
.Restriction gauges are the way to go.


I looked into these a few months ago.., specifically for the 05 Accord.

is it common to have to drill an opening in the post air filter housing? Does it matter where this is/would be positioned? Top mount vs side... Or simply best fit?


Good question. Wish they were integrated as oe.

My car has one built in, but I check restriction with the scangauge once in a while by looking at the manifold air pressure with the engine off, and then WO. I think it was 0.2psi difference last time which I thought was pretty good considering its measuring total intake flow resistance.
 
Originally Posted By: nickolas84
I am refering to stock type "paper" filters. It is common knowledge that the dirtier it becomes, the better it filters.

Should we ever change our stock air filter unless there is a reduction in power?


My career has me in a clean room/clean lab. I get to monitor air quality every day and perform maintenance on extensive air filtration in the lab I work in...to ensure that I can analyze samples down to the parts per billion and trillion.

Here is the bottom line: Yes, the dirtier the filter gets, the filter can trap smaller and smaller particles....thus, becoming a "better" air filter.

As the filter gets dirtier and dirtier, the flow rate across the air filter will change.

One of three things will happen as the filter begins to "clog" up:

1.) the media remains fully intact and the filter begins to collapse, usually causing major leaks to occur where the filter seals along its outside edges; which causing massive amounts of unfiltered air past the filtration apparatus.

2.) air will begin to "channel" through the filtering media, finding a pathway of least resistence. Perhaps it starts at a small imperfection in the media. Once the air begins to channel through the media, the "hole" will expand. The air that passes through this channel isn't really filtered at all.

3.) As the filter begins to clog, the dirt and grit begins to break down the media (cutting it microscopically) and cause leaks to occur in the media...thus, allowing unfiltered air to pass through.

So, my conclusion is: a "seasoned" air filter is better than a new one. HOWEVER, if you run the filter too long, you might as well not have one installed....BECAUSE once the media is compromised, the media collapses, or the air is channeling through it, you have a HUGE source of grit and dirt (trapped onto the filter media) right at the point of failure that WILL get sucked right past the filter assembly.
 
I recently swapped out my reusable Spectre air filter and put in a fram paper element. Never noticed any difference before but the mileage on my last tank was much better and the reusable one never had that effect before. It was dirty on one side so clearly it filters well..but if less air is pulled into the engine wont it increase the fuel sent? Maybe im not understanding it right...
 
Originally Posted By: Rolla07
but if less air is pulled into the engine wont it increase the fuel sent? Maybe im not understanding it right...


The MAF/MAP and the o2 sensor should 'see' that less air is coming in and reduce the injector pulse width accordingly - feedback loops are there to *try* and keep everything working in the correct proportions/ratios with each other
 
Originally Posted By: Phishin
Originally Posted By: nickolas84
I am refering to stock type "paper" filters. It is common knowledge that the dirtier it becomes, the better it filters.

Should we ever change our stock air filter unless there is a reduction in power?


My career has me in a clean room/clean lab. I get to monitor air quality every day and perform maintenance on extensive air filtration in the lab I work in...to ensure that I can analyze samples down to the parts per billion and trillion.

Here is the bottom line: Yes, the dirtier the filter gets, the filter can trap smaller and smaller particles....thus, becoming a "better" air filter.

As the filter gets dirtier and dirtier, the flow rate across the air filter will change.

One of three things will happen as the filter begins to "clog" up:

1.) the media remains fully intact and the filter begins to collapse, usually causing major leaks to occur where the filter seals along its outside edges; which causing massive amounts of unfiltered air past the filtration apparatus.

2.) air will begin to "channel" through the filtering media, finding a pathway of least resistence. Perhaps it starts at a small imperfection in the media. Once the air begins to channel through the media, the "hole" will expand. The air that passes through this channel isn't really filtered at all.

3.) As the filter begins to clog, the dirt and grit begins to break down the media (cutting it microscopically) and cause leaks to occur in the media...thus, allowing unfiltered air to pass through.

So, my conclusion is: a "seasoned" air filter is better than a new one. HOWEVER, if you run the filter too long, you might as well not have one installed....BECAUSE once the media is compromised, the media collapses, or the air is channeling through it, you have a HUGE source of grit and dirt (trapped onto the filter media) right at the point of failure that WILL get sucked right past the filter assembly.


Excellent info on the pitfalls of a willy-nilly, uninformed approach to air filter change intervals.

If you intend extend the OE interval, you shouldn't do so without some forethought. The number one answer is a restriction gauge. You change the filter according to a specified or reasonable restriction reading (15 in. of water gasser and 20 diesel are the low-end generic numbers), you have both headed off any of the bad things mentioned above AND you have gotten your money's worth out of the filter.

The gauge must be mounted downstream the filter but as close to it as possible, ideally in the plenum chamber just behind it. It shouldn't be placed at a bend, near a vortex or close to the throttle butterfly. According the engineer at Filter Minder, they aren't accurate on carbureted engines because of the instable airflow (choke, secondaries, etc.).

Over time and with careful observation, you could probably extend the FCI without a gauge. If, at the OE interval, there is little apparent dirt on the filter, you could extend the interval a ways and check again until the filter is obviously dirty. This can be tricky to gauge because looks are the least accurate way of determining restriction. Once you were obviously dirty, that mileage would then be the modified FCI for your normal driving routine. The danger would be if that routine changed... you took a long trip to a more dusty area, for example. You'd have to be on your toes watching for changes. The gauge is simpler and automatically accounts for all changes.

If there is a long time element involved, that should be factored in as well. In some cases, the sealing material is subject to heat aging and you may get a sealing issue. It really depends on the filter. Look at the cleanable filters for guidance, as their sealing media are designed for decades of service. The sealing material is the best and failure is unlikely. If the replaceable filter used a similar design and material, it's likely good for a long haul. Generally speaking, the foam type seals are the shortest-lived and the type that looks like an o-ring or a seal lip is the longest lived. The OE made this choice for you, so you have to work within the realm of the filter type. Generally speaking, the material in a premium filter is better no matter what the material. In polling various experts, a 5-7 year interval can generally be considered safe for any quality, name-brand air filter. My opinion is, often, the life in years can be a lot longer than that but it's something I'd hash out with a lot of application-specific research for myself.

Avoid molesting the filter seal as much as possible. Every time you disturb it, you risk a sealing issue. For the most part, and this is especially true for the foam seal, they loose pliability over time. They may not fit and seal well on the second (or third or fourth, etc.) fitting. The use of filter seal grease is recommended at the first fitting and during subsequent removal. Not only does it lube the seal so that it fits better, it helps to seal any small gaps and helps keep the seal material pliable. As to the grease, I have not done any research as to whether something other than "filter grease" is viable. Given the K&N filter grease is easily available, I have not taken the time to look past it.

Remember, the engine intake is the primary source for external contamination. A good portion of what finds its way past the air filter makes it into the oil, increasing wear and decreasing oil service life. Much of it is to small to be captured by the oil filter, especially after being ground into polishing paste by the rings. Enough dirt on the cylinder walls causes ring sealing issues and increases blowby, stressing the oil even more fighting the formation of acids from the combustion process as well as fuel dilution.

Finally, installation of a new filter is an important moment. Clean the sealing areas on the housing. Test fit the new filter to make sure it fits the housing well with no gaps. As mentioned above, use filter grease. Then, leave the thing alone as long as practical (note factors above) or the restriction gauge indicates it's time.
 
Originally Posted By: Rolla07
I recently swapped out my reusable Spectre air filter and put in a fram paper element. Never noticed any difference before but the mileage on my last tank was much better and the reusable one never had that effect before. It was dirty on one side so clearly it filters well..but if less air is pulled into the engine wont it increase the fuel sent? Maybe im not understanding it right...


There ya go ,It don't take a rocket scientist to put 2 and 2 together that with a computer controlled engine you will lose gas mileage with a aftermarket reusable air filter ---more air flow signals MORE fuel---If you want fuel economy in your daily driver forget K&N
 
I agree with your comment on fuel being metered in proportion to airflow - at WOT it should make a difference, but I (haven't proven but feel that) a less restrictive filter permits less throttle input for a given torque output, so like most 'efficiency' devices, it permits better mpg when you drive like your grandmother, and more total output when youu drive like you used to when you were 18. Power is the flipside of the economy coin, the potential for either/both usually go hand in hand.
The best analogy I can think of right now is a remap on a diesel vehicle, more mpg than the factory map when you want mpg, and more power than the fdactory map when you want power.

That might not be totally accurate but I'm willing to be educated!
 
There is a direct connection between WOT power and the airflow capability of the intake system, of which the filter is a part. Many times, it's the plumbing that is the limiting factor, not the filter. Sometimes it's the filter but you don't know until you flowbench the system and dyno test. I did flow bench the system on my F150 and it picked up an inconsequential 12 CFM with the stock MC filter element removed from the stock system (633.99 vs 621.58 CFM). With the snorkel & silencer removed it picked up a more consequential 56 CFM (though dyno testing shows this does not increase power without further tuning). Most stock systems can make the airflow a stock engine needs to make rated power, plus a little extra airflow to account for dirt loading, but that isn't universally true. You have to test individually to know.

As to fuel economy, within-the-limits restriction makes little difference in everyday driving. I would refer you to the air filter vs fuel economy test referenced by nickolas84 above at Air Filters vs Fuel Economy. A restrictive filter makes a substantial difference for WOT fuel economy (open loop operation for EFI systems at WOT) but that only matters to race teams. For the average engine operated in everyday "commuter mode" (closed loop) ... the referenced tests, and other information, shows any MPG differences would be inconsequential, if they existed at all.
 
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Originally Posted By: Olas
I agree with your comment on fuel being metered in proportion to airflow - at WOT it should make a difference, but I (haven't proven but feel that) a less restrictive filter permits less throttle input for a given torque output, so like most 'efficiency' devices, it permits better mpg when you drive like your grandmother, and more total output when youu drive like you used to when you were 18. Power is the flipside of the economy coin, the potential for either/both usually go hand in hand.
The best analogy I can think of right now is a remap on a diesel vehicle, more mpg than the factory map when you want mpg, and more power than the fdactory map when you want power.

That might not be totally accurate but I'm willing to be educated!


Gasoline engines have throttles and are more efficient the wider the throttle is open. More power at low throttle openings results in more pumping losses, reducing the efficiency of the engine. This puts you right back to the only benefits of a less restrictive filter being seen at WOT.

Diesels do not have throttles and thus have lower and relatively constant pumping losses regardless of power output. You can't compare the two in this instance.

Ed
 
Originally Posted By: edhackett


Gasoline engines have throttles and are more efficient the wider the throttle is open. More power at low throttle openings results in more pumping losses, reducing the efficiency of the engine. This puts you right back to the only benefits of a less restrictive filter being seen at WOT.

Diesels do not have throttles and thus have lower and relatively constant pumping losses regardless of power output. You can't compare the two in this instance.

Ed


Well stated!
 
Re the two previous posts, spot on. I know about pumping losses and how a diesel uses fuel delivery, not a throttle, to make its power..So its fair to say that you dont need to change your air filter until it sees one of the three conditions in Phishin's earlier post. That'll save me a few quid each year and should reduce the number of contaminants getting into my oil, too!
 
Originally Posted By: Olas
I agree with your comment on fuel being metered in proportion to airflow - at WOT it should make a difference, but I (haven't proven but feel that) a less restrictive filter permits less throttle input for a given torque output, so like most 'efficiency' devices, it permits better mpg when you drive like your grandmother, and more total output when youu drive like you used to when you were 18. Power is the flipside of the economy coin, the potential for either/both usually go hand in hand.
The best analogy I can think of right now is a remap on a diesel vehicle, more mpg than the factory map when you want mpg, and more power than the fdactory map when you want power.

That might not be totally accurate but I'm willing to be educated!


Not quite. Less resistance at part throttle slows the velocity of the incoming air charge thus making part throttle acceleration sluggish and less responsive.
At wide open throttle they are great and might just gain a hp or 2 however due to there being a big hole instead of a tight stream the airflow at low and mid throttle inputs become sluggish.
Leaned this one from experience and this is why cold air intakes are a bad idea on a stockish engine.
 
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