Do Air Filters Affect Mileage?
I was talking with Pat at Tiger Tool recently about whether or not a dirty air filter will actually reduce your fuel mileage. Traditionally, a clogged air filter is thought to rob your engine of not only power but MPGs. But is this theory based on outdated, carburetor technology? Here's how Pat summed it up. It's a little technical for the layman but I'd love to hear what people think:
A MAP based fuel injection system measures manifold pressure to estimate the amount of fuel required by referring to a reference table, doing a few calcs and then adjusting the injector pulse width. The main restriction is the throttle plate downstream of the air filter. Add in the effects of the closed loop system and I can't see why a dirty air filter would reduce fuel economy. I do know that power would be decreased. Also if the program went to open loop or other power mode at reduced vacuum then you would see reduced mileage. I think the whole dirty air filter mileage is a hold over from the carb days where a change in differential pressure across the venture caused a dramatic change in mixture ratio.
Even more so in any system that actually measures air flow through the use of a flap, hot wire or?. The actual air flow is measured and thus upstream changes should have no effect on fuel mileage.
So can we still state blindly that dirty air filters reduce fuel mileage!
Well put, Pat! But I'm sure there is still debate out there. Let's hear it!
I’m sure lube shops who have a vested interest would disagree. Follow the money.
I do think Pat makes a sound argument.
easy to overlook Pats’ observation of less power, as we are discussing fuel economy. also the computer will read the throt.plate position and use in adjustment. changing the air filter should be determined on a individual basis [if you do it yourself]. if you let someone else do it ‘buyer beware’.
I live in an area with a high pine pollen season so I personally change the filters after the season is over. If you do it yourself it is not so expensive.
Oops, looks like the spellchecker strikes again. That should be “Venturi” and not “venture”.
I found Pat’s arguments very persuasive. The computer optimises the engine for a lean burn. Restricting the airflow with a partially-blocked filter will simply cause the computer to reduce the amount of fuel added. Just as Pat said, this will reduce the power available of course.
Then I realised there is an implication in that reasoning. You might be reducing power, but the computer is injecting less fuel into the engine… Might therefore a partially-blocked air filter actually result in LESS fuel consumption through reduced power and so actually INCREASED mileage?
I’m sure it’s not good for the engine, chokeing it like that though, so it is not something that would be good on a regular basis. Does anyone know for certain though if it might actually improve mileage?
Air does not FREE-Flow into an engine. The motor has to provide the power to SUCK the air through the air filter.
More dirt in the filter equals more power from the motor to pull in the outside air.
Throw a blanket over your mouth and try to breath in.
With a dirty air filter, the engine has to work harder just to breath and that equals a loss of horsepower.
The argument of increased fuel mileage with a dirty air filter simply doesn’t make good sense since the constant here is the speed of the vehice and the amount of energy needed to propel and maintain that speed. Bottom line I believe is that to maintain lets say 65 mph, with a dirty air filter more gas pedal pressure would be required to deliver the amount of fuel/air needed to create the same energy that a clean filter and less pedal pressure would provide given that more air is entering the MAP with a clean or K&N type filter. The gas mileage gained I think may be slight if any (1-2 mpg) whereas the power argument is unquestionable to me. I experienced this with my SLK 320 after changing to a cotton gauze filter. I also gained about 1/4 -1/2 inch of pedal while keeping my speed constant.
1. If you were to follow the logical conclusion here, assuming power is not an issue, no one ever needs to change his or her air filter.
2. The statement that electonic fuel injection will automatically optimize fuel and air mixture based upon available air flow is a given. However I would say that the intact mileage belief will be limited to what the engine rpm range will be. With a semi-dirty filter the available air is going to be less than with a new one.
3. Regardless of what we all say, for a car still under warranty, I would religiously change the air filter at the manufacturers interval whatever it is.
all ICE engines are sophisticated pumps. Increasing the efficiency of air flow in any manner decreases pumping losses. Don’t forget the value of having clean air going into the cylinders, along with clean oil in the crankcase.
As pointed out clearly and correctly, the loss of efficiency in the increased restriction of a clogged filter is irrelevant in any situation where the throttle is partially closed, IN ORDER TO DELIBERATELY RESTRICT AIRFLOW to limit engine output and prevent the vehicle from accelerating to its top speed. It might have an effect on those hypermileage vehicles which have no throttle whatsoever and operate by intermittently running a tiny engine wide open to minimize energy lost in airflow, and then coasting. But that doesn’t describe anybody’s street car.
All I can say is that in over 40years of driving, I have never noticed any difference to my mpg when the filter is changed. I have found that climate and using a thin oil have a greater impact on mpg than any other factor.
i noticed even fueleconomy.gov has “debunked” this fuel economy myth.
A clean air filter will not gain you any MPG, _but_ they state it will help your horsepower…..I change mine every 12k….basic paper filter…
put a pillow over your face. Hard to breath correct?
less power.. dirt that passes through the filter gets into the intake then mixed with fuel then into the clean chamber. dirt get wedged between the rings and piston. scoring the walls thus giving you less life out of your engine. less power. correct? let me know if i’m wrong. thanks..
For a few bucks, you buy the oil & air filter combo at
the A-Zone (whiiirrr-whirrrr) and you feel good about yourself and your steed; which is why electric cars won’t make with my generation, either.
REAL men put fossil fuel in that tank, pal; and no sissie synthetic oil for us!
Sorry to whom ever I offend but electric cars will never replace the gas or diesel vehicle. It should not even get the chance to be called a car. If you can’t hear that sweet rumble an engine makes or the ground vibrate underneath your feet. Then it is no car at all.