# 320d/328d air filter



## alacey (Mar 14, 2018)

Any know why the air filters on the 320d/328d have an extra layer of plastic mesh? I have never seen that on any diesel I have ever owned. From what I know from working very closely with Fleetguard when I was at Cummins, it doesn't appear to be for added filtration for air into the engine. The stock filter without this layer seems to be more than enough filtration for the engine.

Do these N47 engines have a crank case ventilation filter? If not, and the vent is near the intake, then that would explain this extra layer being for CCV emissions to ensure no blow by gets out of the engine. This is just my guess. Anyone else know?


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## glangford (Dec 11, 2013)

I had assumed it was for noise abatement not filtration. Someone on either this or another forum put one of those K&N filters on his 328d and noted it was a bit noisier than the stock filter.


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## Doug Huffman (Apr 25, 2015)

Pictured is similar construction to what I recall for my 2000 and 2003 VW TDI***8217;s, though both the TDI***8217;s and my current X5***8217;s additional layer is white.


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## alacey (Mar 14, 2018)

glangford said:


> I had assumed it was for noise abatement not filtration. Someone on either this or another forum put one of those K&N filters on his 328d and noted it was a bit noisier than the stock filter.


That makes sense due to the extent BMW seems to go to lower NVH. If noise is answer, then I would just buy filter without this mesh which is BMW sells for many of their gasoline model and see if their are any efficiency or performance gains. I doubt it, but it wouldn't hurt to see especially since I don't mind a little more turbo noise.


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## Nadir Point (Dec 6, 2013)

Somebody probably just decided a pre-filter to catch the big stuff might not be a bad idea. An adequate pre-filter/filter combo can go a loooooong time in typical pavement environments. The diesel truck guys have been putting aftermarket pre-filters on their rigs since like forever.


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## X3-terrestrial (Aug 27, 2008)

They been like that for a while, not diesel exclusive though.


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## alacey (Mar 14, 2018)

Nadir Point said:


> Somebody probably just decided a pre-filter to catch the big stuff might not be a bad idea. An adequate pre-filter/filter combo can go a loooooong time in typical pavement environments. The diesel truck guys have been putting aftermarket pre-filters on their rigs since like forever.


Yeah, that was the old days with my first tuned diesel truck. Many, like myself, did it because everyone else was doing it thinking it was needed. However, once I got older and started going off of real data rather than what everyone else was doing I saw there was no need for what I was using my truck for. I use my truck on a dusty farm/ranch and many other off road situations like the 8 miles off road I have to go to get to my hunting cabin. My used oil analysis showed no increase in silicon with my AFE Pro Guard 7 filters I use with the pre filter off.

I haven't done a UOA on the car yet. Maybe I will do one with this pre filter and one without it to see if there is any change.


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## Nadir Point (Dec 6, 2013)

alacey said:


> My used oil analysis showed no increase in silicon with my AFE Pro Guard 7 filters I use with the pre filter off.


I don't know what you are trying to measure WRT the prefilter and a UOA, but the only purpose of a prefilter is to extend filter life. Most people are not actually measuring that and throwing away perfectly good air filters on a routine basis. The stuff that gets into the engine affecting a UOA is what happens when a) you use a crap filter, or b) let it load up and it physically fails.

The other demographic is a smaller one that simply doesn't do maintenance. Those are the ones it would help most.


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## alacey (Mar 14, 2018)

Nadir Point said:


> alacey said:
> 
> 
> > My used oil analysis showed no increase in silicon with my AFE Pro Guard 7 filters I use with the pre filter off.
> ...


I am only concerned about once a year intervals when I change my air filter which is about 25k miles on my 328d. If my UOA shows silicon levels no different than with the prefilter versus without it, then I will switch to without it of I see or feel any improvement.


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## Nadir Point (Dec 6, 2013)

alacey said:


> I am only concerned about once a year intervals when I change my air filter which is about 25k miles on my 328d. If my UOA shows silicon levels no different than with the prefilter versus without it, then I will switch to without it of I see or feel any improvement.


I don't think you understood my post you quoted at all. Unless you are measuring air filter restriction with a vacuum gauge or FillterMinder and tracking your change intervals you will never notice any difference except how long it lasts before you need to change it. The only time you could possibly EVER see a UOA effect from an OEM or OEM-equivalent air filter is if it is physically damaged or defective and/or improperly installed.


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## alacey (Mar 14, 2018)

Nadir Point said:


> I don't think you understood my post you quoted at all. Unless you are measuring air filter restriction with a vacuum gauge or FillterMinder and tracking your change intervals you will never notice any difference except how long it lasts before you need to change it. The only time you could possibly EVER see a UOA effect from an OEM or OEM-equivalent air filter is if it is physically damaged or defective and/or improperly installed.


Higher silicon levels in a UOA would tell you that more dirt is getting through the air filter and into the oil. If silicon levels increase with all other variables staying the same, then that is a sign that dirt is getting into the engine. If I test my oil with the current pre filter and then test afterwards without the prefilter and my silicon levels increase, then that is a clear sign that more dirt is getting through the air filter in the time I have it in. I don't care about it lasting longer than my yearly change interval as I stated. If the silicon readings are no different between the two within that time period, then I will go with the one that is either cheaper or provides better efficiency to the point that it pays for itself it is a higher cost.

"Used oil analysis, Cummins notes, can monitor engine oil contaminant levels and provide evidence of dirt ingress, excessive fuel contamination (dilution), coolant leaks, excessive soot accumulation and abnormal wear. For example, elevated levels of *silicon* in the used oil indicate dirt contamination usually caused by faulty intake filtration. The used oil can also contain abnormal levels of copper and lead from bearing material wear, even without extremely elevated levels of chromium and iron being present."

Interpreting used oil analysis

"Silicon Dioxide (sand & dirt) is a common
contaminant ***8211; may indicate a faulty air filter or
seal. May have also entered when top-filling."

The Oil Analysis Handbook


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## n1das (Jul 22, 2013)

The extra layer of material on VW TDI air filters was added when VW eliminated the fine mesh snowscreen in the snorkel to the air box. The snowscreen was notorious for clogging up quickly with debris. The updated filter has an "A" added to the VW part number. It is the cold climate version of the original filter.

I think the extra layer of filter material on BMW air filters does serve a purpose similar to why VW added it. I recommend leaving it alone.



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## Doug Huffman (Apr 25, 2015)

n1das said:


> The extra layer of material on VW TDI air filters was added when VW eliminated the fine mesh snowscreen in the snorkel to the air box. The snowscreen was notorious for clogging up quickly with debris. The updated filter has an "A" added to the VW part number. It is the cold climate version of the original filter.
> 
> I think the extra layer of filter material on BMW air filters does serve a purpose similar to why VW added it. I recommend leaving it alone.


I remember being shocked when I learned about the problem and found the screen - as I recall, in the duct along the left fender - full of carp after I had been so careful to keep the filter changed. And I think that I removed the snowscreen.


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## alacey (Mar 14, 2018)

n1das said:


> The extra layer of material on VW TDI air filters was added when VW eliminated the fine mesh snowscreen in the snorkel to the air box. The snowscreen was notorious for clogging up quickly with debris. The updated filter has an "A" added to the VW part number. It is the cold climate version of the original filter.
> 
> I think the extra layer of filter material on BMW air filters does serve a purpose similar to why VW added it. I recommend leaving it alone.
> 
> Sent from my XP8800 using Tapatalk


Hmm, interesting info. If that is the case, then I don't think it would do me much good in south Texas where it only snowed twice in the last 35 years. Even if it does snow, my rwd 328d would be left in the garage and I would use my 4wd truck.


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## edycol (Jul 8, 2015)

Similar if not same material is used in climates with a lot of rain and/or snow to eliminate moisture levels. 
Maybe that is reason in addition to noise etc. 
M57 engine has it too. 


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## Rodneynelson220 (Jun 17, 2017)

alacey said:


> Any know why the air filters on the 320d/328d have an extra layer of plastic mesh? I have never seen that on any diesel I have ever owned. From what I know from working very closely with Fleetguard when I was at Cummins, it doesn't appear to be for added filtration for air into the engine. The stock filter without this layer seems to be more than enough filtration for the engine.
> 
> Do these N47 engines have a crank case ventilation filter? If not, and the vent is near the intake, then that would explain this extra layer being for CCV emissions to ensure no blow by gets out of the engine. This is just my guess. Anyone else know?


It's a pre-filter for snow. It does make intake a lot quieter but I don't rip it off anymore.

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## alacey (Mar 14, 2018)

Rodneynelson220 said:


> It's a pre-filter for snow. It does make intake a lot quieter but I don't rip it off anymore.
> 
> Sent from my iPhone using Bimmerfest mobile app


Yeah, everything I am reading is that it is mainly for snow which does me no good since it does not snow here but once every other decade. I kind of wish BMW did something like the stock Ram active air intake on my truck which has the ability to pull air from the front directly into the air filter with no bends or from the fender depending on the weather via a flap that closes either door in the filter box. I do notice lower CAC and EGT temps when it pulls air from the front. I also notice better throttle/turbo response too.


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## SmokinCummins (Sep 16, 2018)

alacey said:


> Yeah, that was the old days with my first tuned diesel truck. Many, like myself, did it because everyone else was doing it thinking it was needed. However, once I got older and started going off of real data rather than what everyone else was doing I saw there was no need for what I was using my truck for. I use my truck on a dusty farm/ranch and many other off road situations like the 8 miles off road I have to go to get to my hunting cabin. My used oil analysis showed no increase in silicon with my AFE Pro Guard 7 filters I use with the pre filter off.
> 
> I haven't done a UOA on the car yet. Maybe I will do one with this pre filter and one without it to see if there is any change.


You won't see any differance in the oil sample with the pre filter on or off. The real benefit of the pre filter is ease of cleaning. The pro guard 7 (excellent choice) will not be loaded with bugs stuck between the pleats when you use a pre filter.

I will say I rebuild a lot of 5.9 and 6.7 engines due to poor air filtration. Some of the aftermarket air filters are bad news.

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