The difference a clean air filter makes

[mclasser]

I took a peak at my engine air filter the other day and despite the car not being driven much, it was filthy at 3 yrs/20K miles. I don't live in an especially polluted or dusty environment so Honda recommends 30K miles changes. The car's been to the dealer several times since new but they didn't mention anything in their multipoint inspections. Filters are considered gravy work so I thought they'd jump on the chance to sell me a new one. I picked up a Fram from Wally World and I have to say, the engine feels like its original self again. I lately had to mash on the gas pedal for some extra power but now the car pulls hard like I remember it did when new.

 

[901Memphis]

Placebo effect? You are not supposed to be able to tell the difference between a new and used filter with fuel injection, that goes for HP and MPG, the difference should be nearly un measurable.

 

[NHGUY]

Some vehicles seem to be set up so the filter gets dirty often,others not so much...

 

[Ducked]

Of course a REALLY clogged filter is going to make a difference, but in general engines are surprisingly insensitive to this, especially newer engines where the EMS adjusts the fuelling to compensate.

Maybe fit a restriction gauge?

 

[rslifkin]

Unless the filter is really, really dirty, you can't tell the difference. And even if you can, it'll only be a difference in peak power, so if you're not at WOT, you won't notice anything.

 

[shiny]

Air filters don't make a difference? Really? I'm not necessarily disagreeing, just surprised.

My last oil change switched from Napa semi-syn 5w20 to PUP 5w30. At the same time replaced the pretty dirty air filter with a new Napa air filter.

I keep my tires properly inflated and my driving routine is very consistent. I calculate MPG at every fillup. MPG went from 19 MPG to 20-21 MPG. Is it the new oil or the filter?

 

[eljefino]

Maybe you sealed the airbox better, getting more air passing over the temp sensor, making the computer behave better.

 

[3800Series]

I don't see there being any real difference. I remember someone at some point posting about a filter with over 100,000 miles on it and after being changed they noticed no performance difference not even mileage.

Engines are like a vacuum the dirtier the filter the stronger the suction. As long as they get enough air they work fine. More isn't better so even if the airflow is twice as much as needed there is no real gained performance difference unless you flash the computer to tell the car to take the extra air.

Most filters provide far more air then needed and will still provide good air flow when you replace them.

 

[crazyoildude]

i felt a difference between a motorcraft (which i believe is a purolater also) and a pure one. The pure one was more restrictive i spent over an hour testing both filters on my homemade 1/4 mile and there was a difference. Believe it or not i was there doing the test at my home.

 

[rslifkin]

The air filter can make a difference, but in most cases, they're fairly over-sized. So it takes a decent bit of clogging before it starts to become a noticeable restriction.

Crazyoildude - I'm not surprised the pureone was a bit worse flowing. The oiled paper has always struck me as a little more restrictive.

 

[901Memphis]

Google this for the pdf but I'll paste the conclusion

Effect of intake air filter on fuel efficiency



4.1 CONCLUSIONS
The goal of this study was to explore the effects of a clogged air filter on the fuel economy of vehicles
operating over prescribed test cycles. Three newer vehicles (a 2007 Buick Lucerne, a 2006 Dodge
Charger, and a 2003 Toyota Camry) and an older carbureted vehicle were tested.
Results show that clogging the air filter has no significant effect on the fuel economy of the newer
vehicles (all fuel injected with closed-loop control and one equipped with MDS). The engine control
systems were able to maintain the desired AFR regardless of intake restrictions, and therefore fuel
consumption was not increased. The carbureted engine did show a decrease in fuel economy with
increasing restriction. However, the level of restriction required to cause a substantial (10–15%) decrease
in fuel economy (such as that cited in the literature3,4
) was so severe that the vehicle was almost
undrivable. Acceleration performance on all vehicles was improved with a clean air filter.
Once it was determined how severe the restriction had to be to affect the carbureted vehicle fuel economy,
the 2007 Buick Lucerne was retested in a similar manner. We were not able to achieve the level of
restriction that was achieved with the 1972 Pontiac with the Lucerne. The Lucerne’s air filter box would
not hold the filter in place under such severe conditions. (It is believed that this testing exceeded the
design limits of the air box.) Tests were conducted at a lower restriction level (although still considerably
more severe than the initial clogged filter testing), allowing the air filter to stay seated in the air box, and
no significant change was observed in the Lucerne’s fuel economy or the AFR over the HFET cycle.
Closed-loop control in modern fuel injected vehicle applications is sophisticated enough to keep a
clogged air filter from affecting the vehicle fuel economy. However for older, open-loop, carbureted
vehicles, a clogged air filter can affect the fuel economy. For the vehicle tested, the fuel economy with a
new air filter improved as much as 14% over that with a severely clogged filter (in which the filter was so
clogged that drivability was impacted). Under a more typical state of clog, the improvement with a new
filter ranged from 2 to 6%.

 

[supton]

One time I had a pretty clean filter, but about 5lb of acorns under it.

That reminds me, I oughta check for that again... been finding acorns on top of engine again.

 

[sciphi]

Shouldn't make a difference for most vehicles. Carmakers have gotten pretty good about optimizing intakes for power and MPG these days. Back in the 1990's when they didn't have as much knowledge, it might have made a little bit more of a difference.

 

[DoubleWasp]

Originally Posted By: crazyoildude
i felt a difference between a motorcraft (which i believe is a purolater also) and a pure one. The pure one was more restrictive i spent over an hour testing both filters on my homemade 1/4 mile and there was a difference. Believe it or not i was there doing the test at my home.


Even I fell for this one at first, but I have not been able to find any additional restriction in my testing using both a filter minder, and a real time vacuum gauge. There just isn't any difference in restriction.

 

[KitaCam]

When a dealer told me (after changing the oil) that I "may" need an air filter I knew that they were living down to that stealership reputation when I looked at the filter myself and saw it to be barely gray...

 

[TFB1]

Originally Posted By: DoubleWasp
Originally Posted By: crazyoildude
i felt a difference between a motorcraft (which i believe is a purolater also) and a pure one. The pure one was more restrictive i spent over an hour testing both filters on my homemade 1/4 mile and there was a difference. Believe it or not i was there doing the test at my home.


Even I fell for this one at first, but I have not been able to find any additional restriction in my testing using both a filter minder, and a real time vacuum gauge. There just isn't any difference in restriction.


This^^^

If there isn't a vacuum being pulled the engine is getting all the air it needs to make max power... If even .1" of vac is being created you're loosing power... No not enough for the ole [censored]-o-meter to feel(well maybe here on BITOG)...

Diesels generally have a built in gauge in the air cleaner that indicates when flow is restricted downstream of filter... With a turbo or supercharger a dirty filter can cause a huge power loss...

 

[rslifkin]

Originally Posted By: KitaCam
When a dealer told me (after changing the oil) that I "may" need an air filter I knew that they were living down to that stealership reputation when I looked at the filter myself and saw it to be barely gray...


The "may" phrasing sounds to me like a "we haven't actually checked your filter, but the book suggests changing it at this mileage" kind of thing.

 

[KitaCam]

Originally Posted By: rslifkin
Originally Posted By: KitaCam
When a dealer told me (after changing the oil) that I "may" need an air filter I knew that they were living down to that stealership reputation when I looked at the filter myself and saw it to be barely gray...


The "may" phrasing sounds to me like a "we haven't actually checked your filter, but the book suggests changing it at this mileage" kind of thing.


I know that they checked the filter because one of the bolts clamping the housing WAS MISSING. I had to return to the dealer and have them replace it. They also said I "may" need a cabin air filter....both filters replaced 8 months later only after 2 months of weekly dusty drives through Florida countryside....drives that also ruined the paint on the hood...IT got repainted this week.

 

[WobblyElvis]

Last year I change the air filter on my car with 72,000 miles on the filter. I noticed two things. The car did not need to downshift on hills as it did before. It seemed to produce more power at smaller throttle openings and therefore the PCM would not call for a downshift as often. There was no other difference is power.

Before changing the filter, the throttle plate was getting covered in oil as the added restriction was drawing oil into the plenum between the filter and throttle plate by way of the fresh air breather in the valve cover. After changing the filter the throttle plate remained clean and oil free.

 

[Colt45ws]

Originally Posted By: shiny
Air filters don't make a difference? Really? I'm not necessarily disagreeing, just surprised.

My last oil change switched from Napa semi-syn 5w20 to PUP 5w30. At the same time replaced the pretty dirty air filter with a new Napa air filter.

I keep my tires properly inflated and my driving routine is very consistent. I calculate MPG at every fillup. MPG went from 19 MPG to 20-21 MPG. Is it the new oil or the filter?

Not that surprising. During normal driving, there is a significant amount of vacuum in the intake manifold. Whats the vacuum from? Restriction. Whats the restriction from? The throttle body. Filter companies talk about restriction but your biggest restriction is the intentional one.
When your have a restricted filter, you just open the throttle a bit more and that compensates.
The only time it will make a difference is if you run above 70-80% throttle on a regular basis where you lose all your manifold vacuum. Then the only improvment will be in the power.