All mk3 and mk4 VW TDI used a fuel tank vent in the fuel filler neck to vent air
out. Venting means when you press on the vent to release trapped air to add more fuel to
the tank, extending your car's range per tank. Look inside the filler
neck, you can see a button, see below for detailed pics. Press on it when
the tank is almost full and you will hear the hiss of venting air as you
continue to add fuel. You can get about 2 extra gallons of fuel by
venting.
You can also
remove the vent's spring loaded internals so that you don't have to press on the
button making venting faster. This does not apply to mk5 cars (2005.5+
jetta). Do not do it on a gasoline car. (venting also works on b2 passat and a2 jetta
diesel but those
are pre-TDI and outside the scope of this article) The vent is normally
opened with you put the fuel cap back on.
The only problem venting could cause is if you were to fill the tank all
the way up to the very top of the filler neck and then park the car in the heat.
Heated diesel expands much less than gasoline so the likelihood of
overflowing fuel is very low, but spilled diesel can melt asphalt and should be
immediately cleaned up, so vent at your own risk! If you vented all the
way, just drive a little bit to lower the fuel level and you should not have any
problem with fuel spills. Disclaimer: As with any other information on
this website, it is done at your own risk! This website is not responsible
for damage to your driveway, any persons and/or property resulting from any tips
you found here!
Also note that high flow fuel stations' pumps designed for trucks are larger and can
cause foaming if you fill at their max speed. The high flow large pumps
will not fit all the way into the mk5 filler neck due to a blocking rib.
The mk5 cars don't use this vent either. An mk5 jetta (model year 2005.5+)
fuel filler is pictured to the right.
Do not attempt this on a gasoline car because it is part of their emissions
system, gasoline evaporates much more, and it can create a fire hazard.
The air space may also help prevent fuel spills in a crash when the tank is
full, especially important
with a gas car since gas is more volatile than diesel. The gasoline vapors
are normally trapped and burned in a gas car and the vent helps route vented gas
back to the fuel nozzle instead of into the atmosphere. The TDI does not
use a "carbon canister" or "evaporative emissions"
system.
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Procedure for mk4 a4 body cars (Jetta, Golf, New Beetle), additional notes for New Beetle below Some pics from GeWilli are mirrored here.
Open the fuel filler door and remove the T-20 torx bolt by the filler door lock.
You may want to stuff a rag down the fuel filler to avoid getting dirt inside.
You should now be able to slide the rubber filler surround boot out and slide the entire fuel
filler door out with it.
Set aside to get more room.
The latch strike can also be pulled off. Just gently pry it towards the front
of the car or up.
There is a small tab on the rear of the vent body, push up on it (white
arrow) while pushing the vent button towards the rear of the car (the direction
of the yellow arrow). This should push the white plastic vent
out. On the b5 passat it may be black instead of white. Clean
the o-ring and backflush the vent tube to prevent dirt from getting pushed in
when you put the vent back.
You don't push the black plastic tube out, only the black button and the
parts inside the black plastic tube. It will look like this:
There are two tabs holding the vent internals in the vent body, pull them
slightly out and the vent internals should come out under spring pressure.
You can discard or keep the vent internals, I lost the black plastic ring that
was holding everything in but the internals were going in the trash anyways.
Marked with a white arrow below was where you had to push up during the last
step.
Put the vent body back (minus the internals) and make sure the white tab
snaps the vent body back in place. The vent internals are now removed,
letting you vent faster and easier.
New beetle (NB) additional notes
You can remove the vent in the NB 2 ways. The first way is identical to
the above instructions. The second way may be easier, you remove the right
taillight to get access to the back of the vent. Instructions for the NB
are below.
Open the rear hatch and pry off the oval taillight cover on the inside of the
car. Unscrew the plastic knob that holds the taillight in
place.
Insert a screwdriver at the 8 o'clock position looking at the light to
release a metal clip holding the taillight. Remove the taillight. If the
taillight doesn't come out easily, the clip is still holding the
taillight.
You can now access the vent body from the rear instead of removing the fuel
filler door and rubber surround. The rest of the instructions are
identical to the above. Below is a picture of the vent as viewed through
the rear taillight position.
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