I changed the air filter in my car this weekend (that’s about the limit of my mechanical aptitude, sadly).
What would happen to the car if I just left the air filter out and drove around normally? I’m not thinking of doing it, but I am curious about what the air filter does.
Well, I suppose it filters air. But why is filtered air better than unfiltered air? And is it filtering air that goes into the engine, the air that’s blown into the car when I turn on the vents, both, or neither?
(If it matters for the answer, my car is a '93 Mazda 626. But there are obviously air filters for a number of other cars out there, and I assume air filters perform the same function in all of them.)
A few things might happen… all bad. In some cars, not sure about yours, there is a fiberglass pad that sits under the hood and fibers or actual pieces of this pad might get sucked into the engine… which is bad. Also, and again it depends on which car you’re talking about, the air filter restricts the amount of air that your engine can pull and the engine is tuned based on assuming the air filter is installed properly. Although your car’s computer might be able to compensate for it… it wouldn’t do anything good to your performance, emissions etc.
So the short answer is that nothing good can come from it… and bad things can happen (like random crap being sucking into the intake manifold) so in general I don’t think it’s a very good idea to run an engine without the air filter in place…
Your fuel injection system has a few sensors that measure the air in a few ways (temperature, airflow meter, etc) Dirt can cause errors in the readings and require replacement. Not cheap.
Some fuel injection systems use a “hot wire” airflow meter. Dirt/bugs hitting the wire at high speed could possible break the wire or at least make it useless. Very, very expensive to replace (like $1000 depending on make model, of course).
Fuel Injectors could get plugged as well.
No good can come of it. A $5-$30 air filter is cheap insurance and you should change it every year.
BTW - The only air it filters is for your engine, not cabin air.
I know that the purpose of the mesh is to prevent flames from shooting out of the throttle body in the event of a backfire. But does fuel injection make that so unlikely that the screen is not needed anymore?
I thought the mesh was to keep things like nuts and bolts from dropping down the throat, thus leading to you pulling the intake manifold to get to them. That having been said, I’ve seen many, many cars that have no mesh at all.
As to the OP - the main thing is dirt. The dirt and rocks will plug sensors, pit the valves, scratch the hell out of your cylinder walls, etc.
Air has dirt / dust particles floating in it. Ever see them floating in a sunbeam on a sunny day?
Your car needs to intake air to mix with the gasoline so it will burn. (Remember your high school chemistry–combustion requires oxygen.)
The air/fuel mixture is injected into your engine where there are lots of moving parts. Those parts need to be lubricated so they don’t wear out, therefore you have oil.
Oil, when mixed with enough dirt, becomes sludge and doesn’t lubricate; it gets gritty and sticky.
A sticky engine is bad; it can overheat, seize up, cause undue wear, etc. and probably will leave you stranded at 3 a.m. in the bad part of town.
The air filter helps keep dirt out of your engine. Therefore, the air filter is a good thing.
QED
That Dummies’ Guide, on top of the other info from the thread, is exactly the kind of explanation I needed. Thanks for the info, everyone – and don’t worry, I wasn’t going to try and save $13 by omitting the air filter.
Gosh, my filter has like 10 little torx screws holding the thing in. While it’s not exactly beyond my mechanical abilities, it surpasses my patience-quotient! Be proud; I think the Valvoline place charges me like $20 for a $10 filter.
I am talking about the old standard cylindrical donut shaped filters. They had metal mesh along the inside and outside. But if you had the cover off you could still drop stuff into the carb. I think I may have answered my own question. The mesh may have been to keep the filter’s insides in.
Oh! That mesh, from what I understand, is to provide stability for the filter media, so it won’t get sucked out of place and possibly into the throat of the engine.
Why they don’t use it anymore is that with a fuel injection system, the air filter is typically relocated to a place away from the throttle body, and has a different design and shape than the traditional doughnut-style ones. This different shape allows it withstand the engine vacuum much better, and it doesn’t need the mesh anymore.
It is common to see some speciality cars without air filter elements. They are often driven like this for demonstration or recreational purposes. See this photo:
However newer cars have engines made to much tighter tolerances and have more demanding requirements for air filtration and engine oil. It probably would not hurt your car to drive it a short distance without an engine air filter but you don’t want to do that much.
