Effect of dirty air filter on gas mileage

[rpn453]

Does a dirty air filter affect gas mileage on a modern car?

My thoughts: When the car is warming up and the O2 sensor isn't operational, a dirty air filter could cause the car to run a little rich. But at full operating temp, the computer should compensate for any reduced air flow. A dirty air filter could even potentially increase mileage by reducing power for those of us with heavy feet.

 

[Mike_dup1]

Yes it does. It restricts air to the engine plain and simple which will cause lost perforance and may cause engine damage over prolonged use.

Oil and air filters are cheap compared to the price of repair or replacment of modern engines.

My friend has a repear shop and you would not believe the amoung of people who never change the air filters. 99 times out of a 100 of the cars he sees who won't start or stumble when acellerating have plugs up air filters. He shows me this all the time, it usually results in sludged up engines, fouled spark plugs and a host of other problems.

The engine is not operating efficently.

[ February 09, 2003, 09:14 AM: Message edited by: Mike ]

 

[Pablo]

You were doing OK until your last sentence. The decreased effeciency would offset the lighter foot...and if anything you will need to bury your foot even more to get the same amount of power....yes the feedback loop will try to keep a good, lean stoichemical a/f mix (simplified) - but a) the best ECU is only so good and b) air flow through a clogging filter is not exactly a linear relationship

 

[S2000driver]

Up to a point the ECU can compensate for a dirty filter.

But if you have to crack open the throttle more to get the desired acceleration, on an automatic transmission you will probably downshift sooner because of your throttle position, therefore using more fuel.

On a manual transmission vehicle, most of you fuel loss will be due to the air pumping losses... quite minimal under normal driving conditions.

[ February 09, 2003, 10:28 AM: Message edited by: S2000driver ]

 

[cryptokid]

you guys are missing the secondary benefit of an air filter. this is to smoothen out the air flow so it flows better through the intake.

ok put it this way, you will get more air flow by using a clean, or dirty filter, than no filter at all. this has been proven on a couple of websites i have seen in the past.
they basically dyno an engine with a new filter, no filter, and a dirty black encrusted one. and the loser was awalys not using a filter at all. even a dirty one flows better than nothing.
i figure someone probably doesnt believe me, and i dont have the links to the tests i saw but google search it and youll probably find it.

 

[TheTanSedan]

Stoichiometry is 14.7:1. That is, 14 gallons of air for every gallon of gas.

Why worry over a dirty filter being compensated for by the computer? They're smart, but not that smart -- electronics are not going to overcome a physical deficency.

Air filters are cheap. I change 'em out annually or 20,000 on EFI cars. Unless I've been running dirt roads, beaches, etc., which means change immediately afterwards.

The filters do get holes in them from dust and all. A clogged filter only makes it more likely that a small hole will increase in size.

Guess it would be prudent to buy a car whose service component cost better reflect views on maintenance. This is a non-starter of an issue.

[ February 09, 2003, 02:49 PM: Message edited by: TheTanSedan ]

 

[S2000driver]

quote:

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Originally posted by rpn453:
I know a guy whose Acura Legend used a ridiculous $50 air filter.

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This is what my S2000 filter costs from what I understand, or buy it over the internet for more like $40. These filters have a much more fibrous weave than paper, good quality. Look at them at the end of the road, looks like there's more life left. You can tell that the capacity to hold dirt is really good, because at the end of the life you'll see dirt buildup where the path of least resistance was, but plenty of relatively clean mesh elsewhere.

The filter is already sized for 30,000 or more worth of driving. I wouldn't consider using something else. When changing at the 30K interval, I notice no difference in performance from changing the filter.

 

[Ken2]

The MAF sensor, mass air flow sensor, measure the actual amount of air flowing into the engine. Your engine's computer controls don't know any difference between a clogged air filter and a partly open throttle plate. The fuel/air mixture is correctly maintained for best fuel mileage and clean emissions, and usually not Stoichiometic for emissions reasons.

The high resistance air filter does make a difference for fuel economy at higher speeds when the throttle is quite open...the engine devotes more of it's power to pumping air in than it would with a clean filter. More of that power is going to pull air in and less to the driveshaft, so fewer miles per gallon.


Ken

 

[S2000driver]

quote:

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Originally posted by Ken2:

The high resistance air filter does make a difference for fuel economy at higher speeds when the throttle is quite open...the engine devotes more of it's power to pumping air in than it would with a clean filter. More of that power is going to pull air in and less to the driveshaft, so fewer miles per gallon.

Ken

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I agree. Most of the pumping loss in a gasoline engine is at the throttle plate. Only at wide throttle openings does something else pose a significant restriction.

[ February 09, 2003, 05:43 PM: Message edited by: S2000driver ]

 

[rpn453]

Many good points, and you may be right, but I'm still stubbornly hanging on to the idea that the computer can adjust for the problem. It is able to adjust for altitude and air temperature, I would think it should be able to adjust to what essentially acts as a less open throttle.

I do change my air filter regularly because it's so cheap and I like to maintain performance. However, I know a guy whose Acura Legend used a ridiculous $50 air filter. If you didn't care about performance (there are some who have never used full throttle on their car), it may not be worth changing as often as a normal $5 filter. Of course, I'd personally just modify the intake to incorporate a bigger, cheaper filter!

I'd like to see the EPA throw a car on their dyno and do a new filter vs very dirty filter comparison. If we had emissions testing here I could try to pass an e-test with an extremely dirty filter. If you could pass an e-test with a newer vehicle using a very dirty air filter then that would show that the engine isn't running significantly rich.

 

[VaderSS]

The computer will compensate to a far better degree than a non-computer controlled carburetor will.

From experience, the EFI equipped vehicle's mileage will degrade far more quickly than a non-efi equipped vehicle, but it will happen with more mileage before the degradation begins.

 

[Dr. T]

Does it stand to reason then that, filters like K&N increase fuel economy by lessening the restrictiveness of air filtration over a paper one???