Date:         Thu, 12 Oct 2000 16:35:15 +1000
Reply-To:     Stephen Overmyer <s.overmyer@UWS.EDU.AU>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Stephen Overmyer <s.overmyer@UWS.EDU.AU>
Subject:      Re: Gas Tank Thump
In-Reply-To:  <200010111907.GAA09357@ob1.uws.EDU.AU>
Content-Type: text/plain; charset="us-ascii"

At 15:10 11/10/00 -0400, you wrote:
>From:    Robert Osborn <OsbornSmyth@GATEWAY.NET>
>Subject: Gas tank thump?
>
>  For a while, my gas tank (I think it't the tank..)  has often  made a
>metallic thumping sound,  shortly after startup,  and then a couple of
>minutes after I have parked, and turned the van off.  I have thought that it
>was just the tank contracting when the fuel pump came on,  and then
>uncontracting.  Since I have noticed no other gas tank relatied problems, I
>have just left it the way it is.  Sometimes it makes the same sound when I'm
>filling the tank,  which dosen't alarm me too much either.  Should I be more
>concerned about this?  If it can be fixed,  should it be fixed?  I have
>noticed no change in gas consumption, or any other sign that something is
>wrong.  Anyone else had this experience?


 Sure have,BTDT.Your fuel tank is not breathing in properly as fuel is used
 and the thump is as the negative pressure inside finally overcomes the
 partial blockage and air rushes back in.Not desirable in the long run as
 eventually the tank could split at the seam from fatigue(in an extreme case)

 The blockage can usually be traced back to the charcoal cannister and those
 two little tubes that come off the top of it back up into the engine bay.

 Locate charcoal cannister in rear right wheel well.Remaoval of wheel isn't
 entirely necessary,but jacking up van will give improved access.

 Undo large hose clamp that holds cannister to body allowing cannister to
 drop down.The tube on the bottom of cannister will pull out from the
 chassis.It's only short.

 On the top you will see one larger diameter tube that leads directly to
 the fuel tank.This is unlikely to be the cause but check it anyway by
 blowing some air thru it with the fuel tank cap removed.
 You will also see two small diameter tubes,one purple & one white from
 memory.This is most likely where your problem lies as the tubes block up
 over time with charcoal from the cannister.

 Remove the two tubes (noting which one goes where) from the cannister
 and also from the throttle body in the engine bay (front RHS of eng.bay)
 Clean tubes out with a thin wire and while the charcoal cannister is out,
 give it a vigorous shake for good measure.

 As usual,re-installation is the reverse of removal and then your"thumping"
 should be gone.

 I have had this problem twice.The first time I only gave the small tubes a
 bit of a prod with wire and it fixed the problem...briefly.Then the symptoms
 returned a few months later.
 The second time I did the full thingy as above and all has been well ever
 since.Only took about 30 mins.

 Disclaimer: I am assuming that US spec vehicles will be the same as mine
 with respect to the configuration of the cannister & tubes but as I remember
 a wise man one saying : "To assume makes an ass out of u & me"
 So visually check first...

 Cheers,
 Steve O.
 Blue Mountains NSW,Aust.
 '92 Transporter WBX Kombi
 '76 Transporter Double Cab
 '68 Beetle
 '00 Transporter 5Cyl Double Cab (work truck)
  Fairmont M-19 Speeder