Charcoal Air Filter for Gas Tank

Subtitle:  Charcoal Air Filter for you Gas Tank

I have had a gas smell in my garage for some time now.  I know I don't have any gas leaks in my fuel system... no leaking gas tank, no leaking fuel lines, no leaking carburetors.  How do I know?  I have a new aluminum fuel tank, with a all new fuel lines, new AN fittings, and fuel injection..... and, I've crawled all over my car checking.  Where does the gas smell come from?.... gotta be the fresh air vent from the gas tank.  So what to do?....  

The first thing I did was to add a vapor check valve from Fuel Safe to the gas tank vent line.  These check valves allow the tank to breath fresh air as the fuel level goes down... it needs to to replace the displaced fuel with air or your gas tank would eventually collapse... or the fuel would stop allowing the fuel pump from taking fuel from the gas tank becuase of the vacuum build up in the tank.  Anyway, the tank has to breath.  But the vapor check valve lets the tank breath in but prevents it from exhailing (metaphorically speaking) the gas fumes.  If there is considerable pressure, such as on a hot day, the pressure will overcome the check valve and allow the tank to expell the pressurized fumes to prevent the gas tank from popping... or driving fuel out of the tank through some exit point... which is never good.  Having put in the vapor check valve, the gas smell in my garage was reduced by roughly 70%.... so good, but not great.  

What do new cars do?  They all have charcoal filters on their fuel systems to prevent fuel smells!  Okay, so I'll just buy a aftermarket charcoal filter to add to my air vent line..... simple.  Not so fast.  I spent hours seaching the internet, and talking to automotive guys, and could never find an aftermarket charcoal filter.  So I looked at the original equipment charcoal filters for a number of cars.  What I found was..... to big, wrong shape, to many connection points, to expensive, can't replace the charcoal..... no easy answer there.  I began to wonder how they engineered these?.... couldn't be too tough could it?  So, I bought a used one on Ebay and cut it open to find out what secrets the Toyota's had lurking in their charcoal filters.  Turns out, I was right there isn't any magic. 

Next step was to find a good location for a charcoal filter and build one.  I decided that there was a good spot behind the differential... up high... the panel that serves as the front panel of the trunk compartment.  Then I made a cardboard mock-up that would fit in that space. (I love making up stuff with cardboard... fun!)  When I put the aforementioned vapor check valve plumbing in, I put an AN bulkhead fitting on the rear trunk compartment in anticipation of adding a charcoal filter. 

Having designed the charcoal filter container to fit the space... I carted it off to my favorite fabricator.  Chris Mack, owner of Maxinnovation, took my design and, as usual, turned it into a piece of aluminum art.... which will also work nicely as a charcoal air filter.  The cannister is designed to have replaceable charcoal.  The best I can tell, the charcoal in the Toyota charcoal cannister that I bought is just plan ole charcoal.  So, a run to the local hobby shop snagged a jar of charcoal filter used in fish tanks... this charcoal will be used for a much nobler purpose that filter fish tanks!  I then enlisted my lovely bride to make a pouch to hold the charcoal... she hates sewing so this is easier said than done.  Anyway, having collected the charcoal cannister, charcoal, and charcoal pouch... I put it all together, ran a bead of silicone sealer around the removeable cannister lid... and installed it.  I've plumbed it all with AN hardware... certainly overkill, but I think I've established long ago that I love overkill. 

A couple of points about my design of the charcoal cannister.  It has a removeable lid to allow changing of the charcoal at some point in the future.  Since I planned on placing the cannister under the car, and there is a chance that it could be subjected to water... I have the end exposed to the atmosphere build to shield the charcoal from water and to provide a water vent should water get it.  

I can't yet comment on the effectivenss of this device as I hadn't been driving the car for a while so it's unclear that I have an gas fumes to deal with at this point.  Time will tell.

Steve Thomton

First published 04-07-2012