Fuel vent FAQ for mk3 Volkswagen 1996-1999 VW Passat and Jetta TDI
difficulty: 1/5
back to 1000q: mk3 " how to" index
----- to see the mk4 TDI vent FAQ, see 1000q:
mk4 venting for Jetta/Golf/New Beetle and Passat
Introduction
All mk3 and mk4 VW TDI used a fuel tank vent in the fuel filler neck to vent air out. Venting is 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 and 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 air venting. This lets you add about 2 extra gallons of fuel. Venting does not increase fuel economy at all, it just lets you add a little more fuel to increase miles per tank.
You can also make venting faster by removing the vent's spring loaded internals so that you don't have to press on the button. 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.
Caution: Do not do this on a gasoline car. Your TDI vent is connected to only the fuel tank at one end and the filler neck at the other. It's not connected to anything else. A gasoline fuel tank is connected to an evaporative emissions system and removing the vent will cause a fire hazard!
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. 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!
Truck high flow fuel pumps 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 (pictured right). The mk5 cars don't use this vent anyways.Again, 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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Fuel vent procedure on VW TDI
Here is a video of vent removal on a similar TDI with the fuel tank removed
for illustration. Not shown is backflushing the vent of any dirt before
putting the vent body back. The Passat vent is screwed in and is slightly
different. Do not do this on a gasoline car!
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 another hose at
the top that should just pull out.
Clean the dirt out and then clean it again. I suggest putting the fuel cap back on and hold your finger over the overflow tube to prevent water in the fuel.
Below notes are Passat TDI specific, for Jetta TDI fuel venting, see below
Reach under the wheel well and unscrew the white plastic knob. Push on
the vent towards the rear of the car towards the white knob
was. The vent will come out with the hose. Use some carb or brake cleaner to backflush the tube towards the rear of the
car. The vent tube will be
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. Here is a different view on a similar
TDI with the
vent body halfway out.
The vent body should come out the left side of the vent tube. I suggest backflushing the tube with carb or brake cleaner 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.
Marked with a white arrow below was where you had to push up to release the
vent body out of it's tube.
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.
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