Cleaning the Snow Screens in the Phaeton Air Intake [TOC, Photos done]

[PanEuropean]

I was invited to watch the technicians at my VW dealership perform the 32,000 km (20K mile) service inspection on my car last week. One of the most interesting things that I learned is that Phaetons, along with all other VW products sold in ‘cold’ climate regions, come equipped with snow screens on the engine air intakes.

The purpose of the snow screen is to block frozen snow and ice particles from entering the air filter plenum. If snowflakes or ice pellets entered the plenum and then settled on the filter, they would melt, thus making the filter wet, and this would compromise both the strength and effectiveness of the filter. The snow screen traps particles at the entry to the plenum. They will eventually melt and the water will disappear through a drain hole at the bottom of the plenum.

If the snow accumulation is heavy enough to block the snow screen, the increased vacuum in the plenum will cause a spring-loaded relief valve to open up and admit air into the plenum from the area under the hood, where no snow could be. This is generally harmless, but will cause a slight drop in peak engine performance because the engine will now be using quite warm air from under the hood, rather than cold (ambient temperature) air that is collected from just behind the grille.

The snow screens work very well. In fact, one common problem is that they work TOO well – they tend to plug up with insects, small seeds, bits of grass, and other stuff that works its way along the air intake system to the air filter plenum.

I was a bit surprised to see that the saturation indicator (production code 1L2) on each of my air filters was fully red, implying that the air filters were 100% dirty. The saturation indicators are little vacuum gauges located downstream of the air filter media that measure delta P between the throttle body intake and ambient air pressure.

Air Filter Saturation Indicators
These are only visible when the covers have been removed from the side of the engine.

The techs removed the two air filters, and to tell you the truth, the filters themselves didn't look all that bad. Once we had a look at the snow screens, though, it was obvious to all of us that the snow screens needed to be cleaned.

To get access to the snow screen, the top cover of the air filter plenum is removed (this is the part that has the saturation indicator built into it), and the air filter is removed from its holder. The snow screen is then found at the lower forward area of the air intake plenum. It is held in place with one Philips screw. When removing the snow screen, take note of how it slides into the little rails molded into the lower plenum assembly

Finding the Snow Screen

Left side of engine, snow screen removed

Right side of engine, snow screen removed

The snow screen itself is easy enough to clean – just rinse it backwards with running water, then gently clean both sides of the very fine screen with hot soapy water and a soft brush. If there is any accumulation of sand and debris in the lower part of the air filter plenum, that will need to be removed with a shop vacuum before washing the lower plenum with hot soapy water, otherwise, the debris might clog the water drain when you wash out the lower plenum assembly. There is a water drain in the lowest point of the plenum, and the water should freely and rapidly run out from this drain when you are washing the plenum interior.

Cleaning the Lower Plenum and Snow Screen

Re-assembling everything

Don't forget to reinstall both snow screens, and to reset the two saturation indicators back to zero by gently twisting the dial until the red indication disappears.

I do not know if snow screens are provided on cars that are built for warm weather climates. Every VW I have ever purchased in Canada or Switzerland has been equipped with a snow screen.

Michael

[dcowan699]

I wish our techs would let us go to the back and watch like you get to do. Our laws and rules won't allow us in the back where the techs are. Sometimes they bend the rules though. You seem to really have a cool setup as far as that goes. Wouldn't happen at my dealership (I don't think). My tech likes me and I don't think he'd have a problem with it, it's just the rules that wouldn't allow it.

[PanEuropean]

There is a sign on the door of a very big (and very new) VW dealership near my home that reads: "You are welcome to visit the service area, please ask a service adviser to accompany you". They even have shop coats and little bump hats (sort of like a miniature construction hard hat) for the customers to wear when they are visiting the shop.

My experience has been that the technicians at all VW dealerships are generally quite happy to have customers visit, as long as the customer is accompanied by a service adviser. I think it takes a lot of the mystery and suspicion out of auto repair costs if the service adviser can invite the customer into the shop area, introduce the customer to the technician, and the technician can show the customer what is being done, how the parts work, why certain parts need to be replaced or why certain work has to be done, etc.

The snow filter cleaning was done for me free of charge, however, if the car was out of warranty, it would probably take the technician about 45 minutes to clean the two filters (it is a real PITA to remove the upper air filter plenum covers on a W12). Now that I have seen the extent of the work required, I won't be concerned about seeing a charge for this on the service invoice after the warranty period is finished.

Michael

[W126C]

If I get the chance in Chicago, we'll see if the snow screens are on my car. I'll bet nothing was done to mine down in Texas, if they are there.
Regards,
Brent

[PanEuropean]

Quote, originally posted by W126C »

I'll bet nothing was done to mine down in Texas...

Do they even know what snow is in Texas?

[Jack Orr]

Now, now, Michael. I seed it ounct.

[GripperDon]

Wow what dirty Snow!

[pretendcto]

I decided to replace my phaeton's air filters yesterday since the service indicators were both red. I observed a few things and I thought I would share them with you.

There are 2 different sets of air filters for the Phaeton. A cold (correction: dusty) climate set which has foam on the bottom and a warm (correction: non-dusty) climate set which doesn't. Additionally, the 'snow screens' that sit in the intake snorkels were both completely clogged on my car. The actual filter element had very little debris because of these screens. I'm not sure if all phaeton's have these screens, or just cold climate cars.

I've decided to run the filters without the foam and with no snow screens in the intake snorkels during the summer. I will re-install the screens and winter filters when I change to my winter wheels.

The car runs noticeably better and the service indicators are staying white instead of red after plenty of spirited driving.

Paul

Service Indicator

Inside the Airbox (snow screen on left)

Dirty Snow Screen

'Dusty Region' vs 'Not Dusty Region' Filter - Bottom (corrected: see post below)

'Dusty Region' vs 'Not Dusty Region' Filter - Profile (corrected: see post below)

Modified by pretendcto at 7:20 AM 9-19-2006

[W126C]

Paul,
Very interesting. We'll see what the filters look like come fall. Any way, looks like another spring cleaning project I need to do.
Regards,
Brent

[Motorista]

Thank you for the interesting post, Paul! Two quesrtions: how many miles do you have on the car, and why did you choose to do it yourself (instead of VW service), as I presume your car is still under warranty?
Stefano

[pretendcto]

Quote, originally posted by Motorista »

Thank you for the interesting post, Paul! Two quesrtions: how many miles do you have on the car, and why did you choose to do it yourself (instead of VW service), as I presume your car is still under warranty? Stefano

My car just had it's 20,000 mile service and it shows 19,505 on the odometer. I had noticed the air filter service indicators were both red but left them figuring it would be taken care of. Well, when I got home, I checked and the air filters hadn't been changed. A quick look at the service schedule and I saw that the first scheduled change is at 40,000 miles. By the way, the old air filters seem very clean. I believe my problem was the clogged snow screens.

Interestingly, the service indicators in the airboxes appear to be actual barometric sensors, not something crude. And, after a few hundred miles, I'm happy to report the service indicators are still completely white and the car is running strong!

[Motorista]

That's quite interesting - I'm aspproaching 15kmiles, and indicators still completely white - I'll start watching them more closely.

[PanEuropean]

Hi Paul:

Thanks for the pictures and instructions for the V8. I merged your thread onto the end of a similar post I made concerning the W12, now we have everything in one spot.

Michael

[PanEuropean]

Also - I wrote the engineers in Dresden a few months ago to ask about snow screens - whether all Phaetons had them, or just the Phaetons exported to 'cold climate' countries. Their response was that snow screens are only provided on vehicles exported to 'cold climate' countries. All of North America is considered a 'cold climate' region.

This means that an owner who uses their car in a warm region of North America (e.g. Florida, Arizona) could remove the snow screens without causing any problems - although it would probably be a good idea to retain the screens and re-install them when the car is sold, just in case it winds up going to a snowy region of the country.

The purpose of the snow screen is to prevent large quantities of very dry powder snow from entering the filter plenum. If large quantities of powder snow are ingested, the snow will melt on the filter element and cause it to become soggy and deteriorate. This problem does not arise with the conventional 'wet snow' that we get in most regions of North America - it is specific to very dry powder snow, the stuff that mountain skiers crave.

Michael

[pretendcto]

Quote, originally posted by PanEuropean »

Hi Paul: Thanks for the pictures and instructions for the V8. I merged your thread onto the end of a similar post I made concerning the W12, now we have everything in one spot. Michael

Thanks Michael. I had remembered that post but I couldn't locate it the day I posted mine since the search engine was reporting that it was unavailable. Paul.

[PanEuropean]

Don't feel bad, I tried to merge the two threads three days ago, but couldn't find the one I made because the search engine was not working. The Vortex search engine is - uh - hopelessly unreliable, and that's being kind.

Michael

[Itzmann]

Are there instructions for removing the side engine covers in the manual? I would like to check the status of my air filters.

Thanks.

[PanEuropean]

Hi Francisco:

It is very easy to remove the covers over the W12 engine, however, there are some important precautions that must be taken. I will try to make an illustrated post later today showing how to do this. I am at the German Phaeton owners GTG in Wolfsburg today - there are about 30 Phaetons in the hotel parking lot, so, it should not be too difficult to find a W12 engine to take pictures of...

Michael

[Itzmann]

Michael,

Thanks for the offer for a photographic tutorial... I looked under the hood and it seems there are just a few screws that need to be removed, so it does not look very complicated at all.

However, I haven't dared, because of the precautions you mentioned I need to take... perhaps you could quickly summarize if there is a hidden contact or wire that one needs to beware of pulling out, and what side it happens to reside on?


Modified by Itzmann at 2:46 PM 5-7-2006

[PanEuropean]

Hi Francisco:

Sorry I can't give you a detailed answer - I am in Sudan now and have very poor internet access. The precautions have to do with how you re-install the decorative covers around the engine (one on each side and one across the back) so as to avoid damage to the engine intake cover. I need to post some pictures of this to explain it. I will try to do it in the next week or so, if I can get a connection that allows me to upload a picture. Right now I am on 9,600 BBS satellite uplink, which means text only.

Michael

[Itzmann]

Michael,

You are too nice. There really is no rush. Again, thank you very much for the follow-up.

[PanEuropean]

Hi Francisco:

Here's the worry: If you don't take the time to align all three of the covers around the engine properly when you put them back on, the middle cover (the one at the back) may rub against the air intake and damage the finish on it, as you can see in the photo below.

The way to avoid this problem is to put all three covers on, but not tighten the screws - there are 6 screws total holding the covers in place. Once the covers are in place, just shift the three of them around (they move as a group) until you have the appropriate clearance at the center rear. In the case of my car, I had to shift the covers as far to the right (driver side) as possible in order to get acceptable clearance of that little part that dips down in the middle.

Also - related to the disassembly that has to be done to let you get to the snow screen - there is very, very little space to get the top cover of the air plenum out. Be patient when you do it. Lastly, don't forget to disconnect and re-connect the snap fasteners on the fabric heat shields.

Michael

Watch for rubbing when you re-install W12 engine covers!

[Itzmann]

Thanks very much for the detailed pictures and advice. As it turns out, my car _already_ has the scratch on the air intake I needed to avoid.

I took off the covers and both indicators stood at about the 60% mark (somewhere between the minimum 50% and the midpoint 75%). I did not really have ample to time to continue the disassembly/cleaning job, so I put the covers back on. The car now has over 23,000 miles on it.

Will post here once I do the actual cleaning.

[Paldi]

My indicators were about 85% red at 27,000 miles when I took it in for the 30k service. The dealer said he would replace the filters at 40k miles. My car just turned 28.5k yesterday an I noticed the indicators are now 100% red.

I worry about having to wait another 10k before they are to be replaced. Maybe I should check the snow screens? I am disappointed the dieler did not.

[PanEuropean]

Hi Fred:

Actually, be grateful that the dealer didn't replace the filters. You only get one air filter replacement (free), and if you replace them early (like I did), then you just have to spend the money sooner for the next replacement.

I don't think the dealers know much about the snow screens because there is no documentation in the service manual that discusses them. You can take them out yourself and clean them - it's not at all difficult. Just remember that the snow screen itself is quite delicate, it's best to clean it by holding it under running water for a while, then letting it soak in warm soapy water for a while, then holding it under running water again for a while. If you want to rub it to clean it, be very, very gentle, otherwise, you'll tear the screen.

Michael

[pretendcto]

Quote, originally posted by Paldi »

My indicators were about 85% red at 27,000 miles when I took it in for the 30k service. The dealer said he would replace the filters at 40k miles. My car just turned 28.5k yesterday an I noticed the indicators are now 100% red. I worry about having to wait another 10k before they are to be replaced. Maybe I should check the snow screens? I am disappointed the dieler did not.

My air filters were very clean when I had the 100% red indicators. The snow screens were the problem. I found the job to be very easy, just be careful disconnecting the wire(s) going to the MAF sensors near each airbox.

If you are not comfortable with this procedure, no harm will be done by leaving the situation as it is. The airboxes have spring loaded check valves that will open during high demand to make sure there is enough air flow.

[PanEuropean]

Quote, originally posted by pretendcto »

There are 2 different sets of air filters for the Phaeton. A... set which has foam on the bottom and a... set which doesn't.

Hi Paul:

Thanks for your excellent post and photos. I just got around to reading it now. The difference between the two filters is not 'winter and summer', as you stated, but 'dusty region' vs. 'not dusty region'. The foam layer is added to filter out dirt before it gets to the paper layer, thus prolonging the life of the paper element.

VW designates North America a a 'dusty region'. I'm not sure why - perhaps it is because some cities don't sweep the streets on a regular basis. Anyway, I have provided an illustration from the VW parts catalog that lists the two filters. This illustration is from the section that deals with the V8 engine, but the section that deals with the W12 is exactly the same - two types of filters are shown, one with foam and one without.

Parts Catalog Listing for V8 Air Filters

'Dusty Region' vs 'Not Dusty Region' Filter - Bottom

'Dusty Region' vs 'Not Dusty Region' Filter - Profile

Modified by PanEuropean at 12:59 PM 3-13-2008

[pretendcto]

Quote, originally posted by PanEuropean »

The difference between the two filters is not 'winter and summer', as you stated, but 'dusty region' vs. 'not dusty region'. The foam layer is added to filter out dirt before it gets to the paper layer, thus prolonging the life of the paper element.

Thanks for the clarification on the foam vs non-foam air filters. I just checked my pro-part listing and it also states dusty vs non-dusty region.

[PanEuropean]

Photos re-hosted.

[mhoepfin]

Had my 50,000 mile service recently and it's been bugging me that the air intake monitor was at 100% after that.

Decided to dig in and found my air filters were really clean, but the snow screens were flithy. Took those suckers out for good.. Hey, how much snow do I see in Atlanta?

So I'm wondering if I'll see better mpg without them?

[W126C]

Quote, originally posted by mhoepfin »

So I'm wondering if I'll see better mpg without them?

Hi Mike,
So let us know if you do see any difference. I have thought about removing mine during the summer months here in Kansas, but just had never bothered. Now it just might be worth it?

Chris B, I know that my car sitting in the garage, with or without snow screens makes no difference in my MPG. But that once every three week drive just might save me $0.07 per round trip.
Regards,
Brent

[PanEuropean]

Perhaps a better alternative would be to simply clean the screens whenever you change the air filter. This post explains how to do that: Cleaning the Snow Screens in the Phaeton Air Intake.

If you will never drive in an area where it snows, they can be safely removed. Cars shipped to hot climate regions (e.g. Singapore) do not have snow screens fitted. But, if you remove them, stow them so that the next owner can re-install them if needed.

Michael

[mhoepfin]

I've definitely put them aside for safe keeping.

On my normal trip to work, I usually see about 13.5mpg in light traffic (about a 9 mile commute). Today I was at 15.7 average mpg after that drive. Coincidence?

I'll continue to monitor, but I've got to think having those little red wheels pegged at 100% was having some type of impact.

Also, my air filters looked brand new. Which leads me to think the snow screens were doing the job of the filters.

[PanEuropean]

Quote, originally posted by mhoepfin »

On my normal trip to work, I usually see about 13.5mpg in light traffic (about a 9 mile commute). Today I was at 15.7 average mpg after that drive. Coincidence?

Certainly not all attributable to the snow screens being removed. Car manufacturers sell their firstborn to get a 5% fuel economy improvement - if they could get 20% by removing snow screens, they would not be there, the car would use inertial separation instead.

Michael

[mhoepfin]

LOL. I'm sure there is some placebo effect here with me too, Michael.

But by the same token, to go from 100% restriction to 0% (just checked the dials again when I filled up) by cleaning the snow screens seems extreme.

Are there any metrics around the performance hit when those are at 100%? Is that measure even significant?