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I haven't replaced my engine air filter ever since buying the car used 4.5 years ago and don't know when if ever the previous owner replaced it. A lot of casual car-owners I ask don't even know about the engine air filter replacement. Gas mileage and power seem likely to decrease with a clogged air filter, but why is not replacing also bad for the car (please be as specific as possible)?

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    Btw, there's no reason not to. It's really easy to do. Go to your nearest favorite auto parts shop, they generally have an entire section of filters with a book for you to look up the one that fits your car, spend the $15 on a filter and pop it in in the parking lot. Takes about 30 seconds. It's easier than changing windshield wipers, that's for sure. Your manual should have a page that tells you exactly how to change it. Usually requires no tools.
    – Jason C
    Jul 29, 2016 at 0:04
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    I'd worry more about the oil filter. A clogged air filter will restrict the performance of the engine, a clogged oil filter & dirty/old oil will be doing mechanical damage to the engine. The additives (active ingredients) in the oil only last so long, after that they are no longer providing protection.
    – John U
    Jul 29, 2016 at 10:00
  • What will happen to you if you do not clean your nose for a year? Thats what happened to your car. If your car was alive I believe that could be considered a torture (a full crime)! ☺️
    – Iman Nia
    Dec 2, 2016 at 23:17
  • Maybe one of the auto shops have did that for you and You were not aware that they did it, Most of the times that I go to a shop they check all the filters and change them if it is needed. My favoraite autoshop also checks windshield water reservoir.
    – Iman Nia
    Dec 2, 2016 at 23:21

4 Answers 4

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There are two major problems incurred by not changing your air filter:

  1. As your air filter becomes full of dirt, pollen, crap, what have you, it becomes a restriction on the air inlet. This will degrade performance on the vehicle (as you stated). This will cause you more wear and tear on the engine (having to push the engine harder for it to make up the difference). This isn't a thing you'd notice right away, but rather something which would take effect over a long period of time.
  2. As the filter becomes saturated as stated above, it will only be able to hold so much. When it gets to a certain point, new dirt will start pushing old dirt through, which gets inside the engine. This creates more wear and tear on the engine, which means its useful life is shortened. Also consider, if a filter becomes so saturated to the point the restriction is great, the filter can deform due to the pressure differential, which could allow completely unfiltered air to enter the engine. This would cause a lot of damage over time. If you don't change out your filter regularly, you'd never notice this and could be causing your engine an untold amount of damage.

Changing out the air filter will save you time, money, and wear on vital engine components. If you treat your car nicely over the life of it, it will pay you back in dividends by lasting longer and saving you money. Same goes for any type of regular maintenance you should be doing.

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    Could you explain how a dirty air filter could waste gas and wear the engine more? Excluding non common-rail diesels, a dirty air filter will simply let less air into the engine and the ECU will calculate less fuel for it. Basically you lose power. For every day driving you push the throttle more for compensation and don't feel any other effects, no?
    – I have no idea what I'm doing
    Jul 29, 2016 at 8:04
  • If you're sucking dirty air into your engine this could include debris such as dust and grit. This could accelerate bore wear and cause the valve seats to stop sealing as well as they should.
    – Steve Matthews
    Jul 29, 2016 at 9:08
  • Not sure about the wear and tear part but Consumer Reports did a study on dirty air filters and fuel economy and found no impact on engines with EFI.
    – Jason C
    Jul 29, 2016 at 11:16
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    @JasonC - Considering CR's track record, I take just about everything they say with a grain of salt. Not a trustworthy source in some cases, which means to me they aren't a trustworthy source in most cases. They've been shown to have an agenda. JMHO, though. They may be spot on in this case.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Jul 29, 2016 at 12:14
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    @Pᴀᴜʟsᴛᴇʀ2 How about this? fueleconomy.gov/feg/pdfs/Air_Filter_Effects_02_26_2009.pdf
    – I have no idea what I'm doing
    Jul 29, 2016 at 13:36
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When the air filter gets more clogged then the negative pressure in the air-intake will increase with the following consequences:

  • Dirt will get forced trough the filter or small gaps and increases wear on the engine.
  • Through some small leaks in the air line (between the maf and the engine) there will be more "false air". "False air" is air entering the combustion chamber not metered by the maf-sensor. Thereby the combustion process will be disturbed.
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  • WRT your second point, the MAF sensor is located between the air filter and the engine. If there aren't any vacuum leaks between the MAF and the engine proper, there will not be any unmetered air. The air filter and how ugly it is will not affect how much air the MAF is seeing go through it.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Jul 29, 2016 at 15:21
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The worst thing you can do to an engine in regards to the air filter is change it often. I have been to seminars that explain that 75% of the engine damage is done in the first 25% of the air filters life. A clean air filter lets in more dirt than a filter that is dirty. Expensive big diesel engines have air filter restriction indicators that show when to service the air filter. Manufacturers tell you to not service the air filter until the indicator reaches a certain reading. Service manuals even say if the indicator reaches the service level to keep running until the next oil change. All big engine manufactures are telling us this. I am not saying to never change an air filter but don't do it willy nilly.

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  1. It will decrease performance, but only at full throttle. No efficiency is reduced, because unless the car is full throttle the throttle body restricts the airflow anyway. So unless the car is doing full throttle, there is always restriction to the flow.
  2. New dust cant push old dirt in, and with a clogged filter there is no increase in suction. There is only a limited vacuum available at full throttle, the car cant' go over that in any way.
  3. THE ONLY DRAWBACK OF NOT CHANGING: Lower max horsepower. THAT'S IT.
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