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Discussion Starter · #1 · (Edited)
DIY: Cabin Air Filter, the INEXPENSIVE Way!

You already know that BMW Activated Charcoal Filters or Mann Cabin (non-charcoal) Filters are $30-45 per pair of Cabin Filter, which is rather expensive for this low-tech device.
This is a DIY (guaranteed easy!!!) using Standard Engine Air Filter for $6.50/each or $13 total. So you will save $15-30 easily.

1. How Activated Charcoal works:
http://www.howstuffworks.com/question209.htm

- The activated charcoal basically filters out the odors (farms, pigs, cows, NYC exhaust etc.).
- However once the charcoal pores are filled with these odorous particles, then the charcoal component of the filter is saturated and useless, but the Air Filter still filters through pollens, dusts, particles etc.
- The lifespan of activated charcoal depends on how much smelly stuff the filter has to adsorb.

2. As an inexpensive substitute (not activated charcoal):

- Use 1998 Cadillac Deville ENGINE Air Filter as a reference for E39 CABIN Filter. So any of these Engine Filters will work:

- Fram CA6479 ---> $6.50
- Purolator A34479 ---> $6.50 (at Advanced Auto Parts).
- Microguard GA34479 ---> $6.50 (at OReilly Auto Parts).

271 mm x 203 mm x 43 mm
(Stock Size is: 267 mm x 201 mm x 30 mm)


These filters are a tiny bit bigger but all you have to do is: using a utility knife and trim 2-3 mm of rubber molding on each long side and it will fit perfect. You will save $15-30 for beers money***8230;...hehe!

This is the shortest DIY that I ever wrote: 1 picture! Just a way to save some money during this goofy economy....:)



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I think that is great to substitute the air filtersbut I don't mind spending $15 extra for the right fit and function with no effort. Just a difference in perspective and priority I suppose.
 

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I wonder how well it flows air compared to a cabin filter. I suspect the air filter has more impedance to airflow. Remember that the blower motor fan would not generate much suction being a squirrel cage fan.
So, while it may appear to work, there would be diminished airflow. Don't know this for a fact but it seems reasonable to me. Perhaps I'll spend $7 on an experiment.
 

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Wow! at $5 a pop, I won't mind replacing mine more often. I've made mine last 2-3 times longer by just blowing out the stuff backwards w/ an air blower gun set to 45 psi. easy and effective.

Besides that, the last time I used charcoal cabin filters was when it came from the factory that way. Imo, what they're wanting for a charcoal lined filter is just too damn much for something that doesn't do squat. I'd rather divert my car money towards oxygen sensors, spark plugs, thermostat, or wiper blades first b/4 I blow it on cabin filters.

THX cn90! this will be my new cabin filter swapover here on out. Frugal is the new black.:thumbup:
 

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Discussion Starter · #16 ·
i got the fram filter yesterday and i was wondering how did you take off the rubber seal to make the trimming? cause the fram filter and the rubber seal are glued together.
It is easy as 1-2-3.

Do not take off the rubber molding.
You simply use a utility knife or a pair of scissors and trim 2-3 mm of rubber molding on each side as shown.
The whole thing should not take more than 2 minutes!

 

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I wonder how well it flows air compared to a cabin filter. I suspect the air filter has more impedance to airflow. Remember that the blower motor fan would not generate much suction being a squirrel cage fan.
So, while it may appear to work, there would be diminished airflow. Don't know this for a fact but it seems reasonable to me. Perhaps I'll spend $7 on an experiment.
Great DIY idea here. Demonstrating CN90's great ingenuity as always.

Just wondering the same: flow rates and effect on blower operation.

Personally, I'd prefer higher flow rate than lower so it won't increase the chance of blower motor burning out from sucking too hard.:yikes:

Now we can take it one step further and go to a pet store and get some activated charcoal and sprinkle it on the steel wire grate side and have charcoal style filters! When the charcoal loses it's strength. Turn filter over and discard and refill with more charcoal. Reusable charcoal filters!
 

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Discussion Starter · #20 ·
...Personally, I'd prefer higher flow rate than lower so it won't increase the chance of blower motor burning out from sucking too hard.:yikes:....
The Filter Material is essentially the same for Cabin or Engine Air Filter.

The only air filter that is very restrictive is the 3M "Ultra Allergen" Filter for Home HVAC and this significantly reduces the flow of the Furnace Blower, per my Home HVAC repair man. This 3M "Ultra Allergen" Filter traps VERY small aprticles to the point that it can reduce the lifespan of the Furnace Blower Motor:
http://www.sears.com/shc/s/p_10153_...Heaters&psid=FROOGLE01&sid=IDx20070921x00003a

Car Cabin or Engine Air Filter is essentially the same in terms of flow rates.
Don't worry about the Fram or Microguard Air Filter.
It works fine for me.
 
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