Air filter / pre filter / bypass question...

PacCoastFwy923 · November 6th, 2008, 18:48

Ok, the trouble with doing (simple) maintenance on the car with you lot for help is a lot of in-and-out with greasy hands and no patience to search for answers.

So I think I found part of what I was looking for, but it's too late 'cause I took the pictures already.

First two pictures: is this the "prefilter" I see some of you writing about (the dirty fuzzy layer on the old filter on the left). If so, it appears I can continue using the pink filter on the right here in the mild SF bay area, yes?

Good...

New filter 1K0 129 620D on the left and 620E on the right.

No pre-filter vs. pre-filter?

Next question...

What's up with this air filter bypass? And why is it open?

It appears that vacuum should close it, maybe? It also appears that it feeds something other than the engine?

BUT... it also looks as though it can feed the engine air, as well: through the bypass and up, and it goes right into the port with all the filtered air.

So what the purpose and the operation behind this crafty device?

airwolf · November 6th, 2008, 19:24

The flap you are talking about opens when it is cold out. This is supposed to draw air off of the exhaust manifold and help the car warm up quicker. If it is staying open then you have an issue with it.

There have been a couple post on here about a fix for these.

LF06VWJTDI · November 9th, 2008, 05:18

Yes, you can definitely continue using the "D" version of the filter. The "E" version is only for cold climates.

PacCoastFwy923 · November 10th, 2008, 08:30

Thanks, fellas.

Reading through previous posts, it seems that this door should have been closed when I was digging around in there, changing filters. It had to have been at least 65° that morning.

Considering everything else in this car is tied in to the computer, should I see a warning message if the door operation malfunctions?

Is the extra soot / particulate on the last third of the filter noteworthy? That is to say, does it indicate that side of the filter is being used too often?

Am I correct that this bypass allows unfiltered air into the intake?

Thanks again.

SBAtdijetta · November 10th, 2008, 08:41

No it does not let unfiltered air in to the intake. It simply pulls the hot air off the exhaust manifold, then filters it through the filter and into the intake.

I don't know why your filter is so dirty. Maybe you drive in a dusty or construction filled area?

PacCoastFwy923 · November 10th, 2008, 10:12

Quote:

Originally Posted by SBAtdijetta

I don't know why your filter is so dirty. Maybe you drive in a dusty or construction filled area?

Dunno... first air filter change by me, at 44K. We bought the car used in February with "normal" looking VW Dealer service intervals, so I (*cough*) assumed (*cough*) we were in good shape.

Who knows, they might have only been oil & filter changes — this may very well be the car's original air filter.

tdipdphd · December 5th, 2008, 19:39

is there any video or step by step guide in changing your air cleaner filter element around here?

abarns · December 6th, 2008, 04:41

It's been a while since I messed with my car, but IIRC airflow is from the underside upwards, hence the little bypass is filtered. I'd imagine the large amount of black stuff on the filter (on the bypass side at least) is because of the area the air is coming from, i.e. under the hood not from airflow hitting the front of the car. The filter really isn't that dirty on a second look. Also, isn't the service interval for the air filter 40k miles? You're good without the prefilter, you have to have quite a bit of snow to waterlog the filter methinks.

Edit- Changing the air filter- remove the screws holding the top of the airbox on (11 if I remember, but not sure)... they all face upwards and are on all sides of the box. Remove the top of the box, do your best to prevent any dirt from entering the clean side of the box or intake (not hard since it faces downwards). Remove the filter. Insert the new filter. Put the top back on, tighten the screws back down (I don't have the torque spec... I would guess 'snug' would do it). I've seen it recommended on here not to open the filter box until you want to change it in order to not mess up the seal, i.e. don't check to see if it's dirty. I don't know if it's solid advice, but I don't mess with it.

roadhard1960 · December 6th, 2008, 05:17

My maintenance includes vacuuming leaves and dirt out of the bottom of the filter housing. Don't blow the crud out as you might just blow it somewhere it is not supposed to go like the top of the air filter housing.

DidJettarun · December 6th, 2008, 09:57

I just changed my air filter yesterday (during my 100K service)and it looked identical...I also had the door stuck open and we used shims to keep it closed...(my friend the ex-marine diesel tank mechanic says the the hotter the intake air the better it runs and that I should have left the door in the open position to allow hot air off the manifold all the time)by the way that door is not a replacable part according to VW you have to replace the entire airbox assembly ( almost $200)

dhdenney · December 6th, 2008, 10:23

Quote:

Originally Posted by DidJettarun

I just changed my air filter yesterday (during my 100K service)and it looked identical...I also had the door stuck open and we used shims to keep it closed...(my friend the ex-marine diesel tank mechanic says the the hotter the intake air the better it runs and that I should have left the door in the open position to allow hot air off the manifold all the time)by the way that door is not a replacable part according to VW you have to replace the entire airbox assembly ( almost $200)

I'm thinking cooler air will be denser and therefore better for intake. However, I mainly wanted to note I like the prefilter cuz it keeps the **** out of the pleats of the filter.

thaws1981 · July 18th, 2010, 00:15

Does the Air Filter Bypass have anything to do with the EGR? Does the Air Filter Bypass deliver Exhaust Gases back into the Air Intake System?

I have looked in the 2005-2006 VW Jetta Service Manual and the Air Filter Bypass is not shown in the Intake System Diagram.

airwolf · July 18th, 2010, 07:19

Quote:

Originally Posted by thaws1981

Does the Air Filter Bypass have anything to do with the EGR? Does the Air Filter Bypass deliver Exhaust Gases back into the Air Intake System?

I have looked in the 2005-2006 VW Jetta Service Manual and the Air Filter Bypass is not shown in the Intake System Diagram.

No, the air filter bypass has NOTHING do to with the EGR. EGR gasses are introduced directly into the intake via the EGR valve and has no filtration on it. Only thing that happens to the EGR gasses is they get 'cooled' by the EGR cooler ;-).

MyAvocation · July 18th, 2010, 21:42

Yes, correct change interval is 40k. And yes, that's an unusually dirty filter, but isn't necessarily a problem. If no performance increase with new filter, then old one was not overly restrictive.

Mach1 · July 19th, 2010, 00:18

Abarns, I would include one other small detail to your DIY...I have seen the seal get stuck and pinched if they are not placed down in the bottom box..I usually place/push the seal around the entire parameter. So, I would throw in there about checking the seal surface after installing the filter in the bottom airbox-that the seal is down in the seal area...R U enjoying civi life?

I like cool air coming in my filter so I jammed my defective valve shut. I havent seen one yet that was working correctly. They are all partially open at ambient, so I go in there and run a screw in them and preload them, so they are shut..