Dual air filter... I didn't know

[Errtt]

So today I pulled the air filter to get a peek or change, figuring I'll change it today because it's been a good while, wanted to see, knowing miles and times of very dusty conditions, and I'll be changing the oil in a week. So I'll have about 500 miles on it, then oil change comes. If okay, I'd leave it.
So I get the filter out, looks pretty grungy, then wanted to see a little downstream after the filter. I loosen the snorkel clamp and hoses so I can remove the top cover to see how clean/dirty things look. Then I found built into the top housing another air filter, smaller than the main primary filter. It looks like the only way to replace it if it ever comes to that is to buy/replace the top filter box housing - because I can't see an obvious way to remove only the filter media.
I don't recall seeing anything in the owners manual about 2 air filters in the engine compartment. Had I not got curious, I would have never known there was another filter up under the air filter box top cover.
Oh, and I'll soon have an air filter indicator on it's way soon. But two filters?

add - 2010 Hyundai Tucson 2.4L

 

[901Memphis]

Ford focus has two filters. You should only need to replace the one. Check rockauto for replacement components to get an idea on cost and what it looks like.

 

[vssjim]

It maybe a active charcoal type of filter for gasoline vapors and not a filter per say ever needing to be changed

 

[Jim Allen]

Didn't know they had them in cars. All of my farm tractors have two filters, one inside the other. Most things that operate in the dirt have something similar.

 

[901Memphis]

Couldn't find anything on rock auto about the other filter, don't think there is a part for it easily found.

 

[JimPghPA]

Me thinks you are confusing the metal air element that causes laminar air flow, for a filter.

If it is something with many passageways all the same size, and looking something like a metal honeycomb, and they are made out of metal, it is not a filter. Laminar flow of any fluid such as air or water is a flow that has no turbulence and the same velocity anywhere in the stream, which will make it easier for any sensor to give a true indication of how much air is flowing into the engine.

You can search YouTube for "laminar flow" and see some demonstrations of what laminar flow is all about.

 

[Rand]

what car is this?

 

[Errtt]

Originally Posted By: Rand
what car is this?

2010 Tucson

 

[Errtt]

Originally Posted By: vssjim
It maybe a active charcoal type of filter for gasoline vapors and not a filter per say ever needing to be changed


Looks like this may be it - just went over to a Hyundai forum and some have discovered this and some mentioned the same.

I should have taken a pic but didn't think of it at the time.
It looks pleated just like the main air filter, smaller in size, and kind of a light charcoal color I guess. Almost looks like a filter with darken media, like maybe some crankcase fumes got to it (maybe). Not dirty, just darken. A few have taken it out.
Just struck me as strange as I was not expecting it when I went to look up under the air box cover.

 

[gaijinnv]

Here's the air filter box on the 5.7 Litre petrol V8 in my 2013 Toyota Land Cruiser:

Here is a pic of the main filter element (replaceable):

And here is a pic of the second filter in the filter housing cover which is a permanent part of the housing(non-replaceable):

The second filter should never have to be replaced.

 

[eljefino]

I like these 2nd filters. If nothing else, they might stop rodents and rodent by-products.

 

[SOHCman]

We must not be trusted any longer to not get dirt in the housing when changing the filter? I wonder what the other filters rating is?

 

[Smokescreen]

The pics remind me of the charcoal filter found in every Toyota I have seen. It doesn't really filter the air other than prevent any gas fumes from escaping back into the atmosphere once the engine is off, when ever that may occur.

 

[accent2012]

That is definitely a charcoal filter to comply with state/local emission standards.

Most manufacturers do not include them in their cars depending on the region, but they all should include them. My parent's toyota had this charcoal element.

They do not affect hinder the air flow as they essentially do not filter at all and should not be relied upon as a filtering element other than to trap gas vapors.

 

[Errtt]

My filter I'm referring to is not like any of the pics. It is pleated just like my primary air filter - it must have the duty like the ones in the pics, just different (pleated).
I read on another forum that a few have removed them. Heat/melt the plastic buttons holding it in. But then there were a few mixed reviews, same or a little more power, same or better mpg etc.
I'm sure not going to remove mine - it was put in place for a reason. And as long as the primary filter does its job, then the secondary (if you want to call it that) should last many many miles. But in the future, every time I need to replace the primary filter, might as well place a good eyeball on that second filter.

 

[circuitsmith]

When a gas engine (FI or carb) is shut off it's possible for a cylinder to be left standing filled with fuel/air mix and in the middle of the intake stroke, so the fuel/air can make its way back through the open intake valve and up the intake tract.
It's also possible for the PCV system to feed some crankcase fumes back into the intake after the engine is stopped.
These small amounts of hydrocarbons were insignificant in the earlier days of emission controls, but now they have to be dealt with and kept from finding their way to the outside.

 

[Jim Allen]

Originally Posted By: circuitsmith
When a gas engine (FI or carb) is shut off it's possible for a cylinder to be left standing filled with fuel/air mix and in the middle of the intake stroke, so the fuel/air can make its way back through the open intake valve and up the intake tract.
It's also possible for the PCV system to feed some crankcase fumes back into the intake after the engine is stopped.
These small amounts of hydrocarbons were insignificant in the earlier days of emission controls, but now they have to be dealt with and kept from finding their way to the outside.


Brilliant observation!

As a side note, this backflow of PCV gasses (engine running too) is one reason why MAF sensor wires get contaminated. Motor oil isn't a MAF friendly oil, necessarily. If you happen to have an aftermarket oiled cotton gauze filter (K&N), of course, that will get the blame. Even though the filter oil is proven not harmful to MAFs.