Leaky 200 Tank

Tom Werner noonan67 at hotmail.com
Mon Dec 15 08:06:19 EST 2003


I posted almost the very same question about a week ago.  My leak is (was, 
hopefully) above the mid muffler, driver side.

In order to drain the tank, I got a siphon pump from Harbor Freight ($8) and 
10' of 3/4 in vinyl tubing from Lowes ($3 or $4).  I accessed the tank 
through the fuel pump connection in the trunk.  I could not stick a tube 
through the filler neck to siphon, as there appears to be some sort of 
restricter to prevent just such activity.  If your leak is on the driver 
side, you will have to position the siphon tubing to the right area of the 
tank.  The tank has two tiers, with the passenger side with the fuel pump 
lower than the driver side.  However, the driver side of the tank has a 
"sunken" portion that will retain gas even if everything is drained from the 
passenger side of the tank.

I got the siphon going using the Harbor Freight pump, then put the tubing 
into a 5 gallon tank and let atmospheric air pressure (the driving force 
behind a siphon) do the rest.  I had to siphon because my car was still in 
the midst of a timing belt change.  However, if you have 1/8th to 1/4 of a 
tank of gas, take the car out and do a few hard left turns.  This will slosh 
the gas from the driver side of the tank to the sunken portion of the 
passenger side.  Your leak should stop then, simply because there is no gas 
in the tank.

The leading edge of the tank on the passenger side is in an awkward place.  
Tim Leonard (his post is below) was absolutely correct when he suggested 
that debris caught by the heat shield did my tank in.  Seems to me that the 
easiest way to access the tank for repair would be to drop the exhaust.  You 
will then have direct access to the tank and be able to scrape the area, 
clean it and apply the proper sealant.  However, the bolts that hold the 
clamps connecting the mufflers to the rest of the exhaust system had rusted, 
and would probably need to be cut off with a torch.  I didn't want to do 
this with a leaking gas tank.

So, I dropped the control arm on the driver side rear wheel.  This gave me 
enough clearance to access the leading edge of the tank from the side.  I 
scraped off as much rust as I could (very important) and then cleaned the 
area with brake cleaner.

To apply the Seal-All (gas and oil resistant from Lowes, approx $2.50 per 
tube), I used neoprene gloves (also from Harbor Freight).  I would double up 
on the gloves for the application hand (worked out much easier this way) and 
poured the Seal-All into that hand then applied it to the tank.  I spread it 
all over the entire edge of the seam, as well as the areas with obvious rust 
pockets.  I also used some fiberglass tape (from the drywall department of 
Lowes) to hopefully add a bit of extra strength at the leaks.  Whether this 
is necessary or not is debatable.  The Seal-All would take about 20 minutes 
(in 45 degree weather) to harden enough for an additional coat.  I figured 
the more the better, and applied two tubes of the stuff, with a third and 
final tube waiting on a clear and warmer day (hopefully today).

The other option is to replace the tank.  I figured that a minimum would be 
in the area of $800 for just the labor on this job.  I do almost all my own 
work, but there is a lot going on in the rear of the quattro.  Everything 
you can think of has to be removed, including the exhuast and the diff, as 
well as brake lines.  Yuck!

Tim Leonard's post to me is below.  He also had some good advice to check 
while you are under the car.

Hope this helps,

Tom Werner
88 80q
91 200q
92 vw cabriolet

I would bet it (the leak) is driver
side above the rear portion of the forward muffler. The heat shield above
the muffler is pushed tight against the tank right at the seam. It will
collect debris/mud and water at this area and eventually rusts through the
seam area. The rust will spread the seam open making it more susceptible to
more/faster rusting.  The first one I repaired by removing the tank. I spent
allot of time cleaning inside and out, etching the inside and coating the
inside with a tank sealant. A year later it started leaking again. To fix it
the second time I used Seal-All. I was not about to go through the process
again to do it "right". "Right" truly would be a new tank but these cars are
of an age and value that it is not worth the trouble and cost. It has been
fine since and was VERY easy. Another car had the same leak and from
previous experience I used Seal-All. It has been fine since. I would suggest
you use the same product. Remove the heat shield, clean the tank area where
it is leaking and apply Seal-All to the active leak. A good result is a bit
easier if the gas is not actively leaking. You need to be at about a 1/4
tank before it will stop leaking and that is not guaranteed due to the shape
of the tank. You need to get the gas to "slop" over to the passenger side.
Jacking up the drivers side helps. Or go for a drive and do some hot left
turns. This is the only area I have ever seen these tanks develop a leak. I
have seen several. I now routinely remove the shields on cars in for service
and check and clean this area to prevent this from happening. Also, upon
reinstallation of the heat shield I bend the rearward edge away from the
tank so crap won't collect there. It is easier to prevent than to repair in
ALL aspects of Audi maintenance. If you have a hoist it is much easier.
Removal of the exhaust system also makes this job easier and it will come
off quite easily if you have clean (not rusted) bolts. Replace the exhaust
bolts with stainless and use Anti-seize. Also check the forward hanger at
the cat converter. It is usually rusted away. If this is ignored you will
end up with a broken down pipe at the turbo. I have repaired three because
of this. Part is available from the dealer and is cheap. Part #443 253 251 B
and 443 253 268 for the right side and #443 253 267 B times 2 for the left
side of the exhaust pipe. Check all of the rubber hangers as well. They too
are cheap and must be replaced if broken. They are available from any
aftermarket supplier. Part #4A0 253 147 A. I use Tim LeClair @ Foreign Auto
Parts 800.728.1601
Best regards,
Tim Leonard

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