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 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.
Jetta sedan - normal capacity: 14.5, vented: ~16.5
Passat sedan - normal capacity: 18.5 gal, vented: ~22 gal
Passat wagon - normal capacity: 21 gal, vented: ~27 gal
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Procedure
Remove the fuel cap and stuff a paper towel in the filler neck to prevent
dirt from falling in. Remove the circlip spring from the outside edge of
the rubber gasket. The circlip is a 270o metal
spring that holds the rubber surround in place.
Remove the rubber
surround. There is a drain at the bottom and there is the fuel overflow tube at
the top that should just pull out.
Clean the dirt out and then clean it again. I would put the fuel cap
back on and hold your finger over the overflow tube to prevent
water in the fuel.
Below notes are passat specific, for jetta, see below
Reach under the wheel well and unscrew the white plastic knob. Push on
the vent towards the rear of the car where the knob
was. It should come out with the hose. Use some cleaner to backflush the tube towards the rear of the car, it'll be very
dirty and you don't want debris going into the fuel filer neck when you put the
vent body back.
You should also clean the o-ring on the vent body and the
vent body to prevent dirt from getting into the fuel.
There are tabs that hold the vent in place, gently pry them
to remove
the vent internals. Below is another picture (from a jetta, ignore
the white arrow) showing the tabs.
Put the vent body back and screw on the knob to hold the vent body in
place. Make sure to replace the fuel overflow tube at the top right of the
below picture and to make sure the drain in the rubber boot is clear.
The vent internals are now removed, letting you vent faster and
easier. Passat procedure ends here, the below notes are specific to the Jetta.
Jetta specific procedure continued here
There is a small tab on the rear of the vent body (white arrow below), push
up on it while pushing on the button towards the rear of the car. This
pushes the internals towards the rear of the car (yellow arrow). This should push the white
plastic vent body out. Clean the o-ring and the vent body to prevent dirt from
getting into the fuel.
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:
The vent body should come out the rear of the vent tube. I suggest
backflushing the tube towards the rear of the car to clean out any dirt in the
tube. 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. Make sure to replace the fuel overflow tube at the top right of the
below picture and to make sure the drain in the rubber boot is clear.
The vent internals are now removed, letting you vent faster and easier.
Do you have any questions about this procedure? Post your
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