Fuel tank expansion chambers.

[golfingtam]

Hi, Can anyone help me with my problem? I would like to know if any fluid /petrol expands into these chambers under the front wheel arches. I have fitted a new fuel tank and replaced the breather hoses and would like to know the answer to this. Thanks.

[Mocki]

No, only vapours .
If they were not there, you would only be able to fill the tank half way

[maxstu]

No, only vapours .
If they were not there, you would only be able to fill the tank half way

Really? Not had both sides fitted for eight months. Fills all the way. New tank, seals and fuel lines too. Slight smell coming from filler cap when it was warm last week.
Fuel injection tank

[Mocki]

Well are you sure it’s filling all the way up ?
I’m guessing you haven’t sealed the breather holes up and vapours can escape into the atmosphere.(;which isn’t good)

[R0B]

If they were not needed why did VW feel the need to put them there?

[maxstu]

Well are you sure it’s filling all the way up ?
I’m guessing you haven’t sealed the breather holes up and vapours can escape into the atmosphere.(;which isn’t good)

Correct. Rarely filled beyond 3/4. Old habit l guess.
I linked both side with a six inch length of fuel pipe. Not intended as a permanent set up. Mostly for repair welding around these areas. But it makes it is so much easier to work around the wheel arches. And no more build up of dirt

[maxstu]

If they were not needed why did VW feel the need to put them there?

Just because something exists, does not necessarily mean it is needed. Yet perhaps they are needed in extra hot countries where fuel vapour expansion may cause issues?

[Mocki]

By the shape of the tank , when you tried to fill to the top air ( vapours) would be pushed to the top of the high points of the tank , airlocks , and with out the breathers and expansion tanks the filling would stop before full .
Like wise when the ambient temperature rose there would be nowhere for the expanding fuel and vapours to go to . The filler neck is only in one side in the tank to allow that breather to tank the expansion From the other side high point


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[maxstu]

Yes. I see. Good information with thanks. I do intend to reinstate sometime. By shape of tank, reckon filling 7/10 without vent containers in place is okay.
Im going to run camper without them in winter though. Both are corrosion traps

[Aidan]

because of the shape of the tank when the vehicle is going up a hill the fuel moves to the back of the tank and vice versa, and side to side the same, the breathers allow the vapour in the tank to balance regardless of angle and prevent pressurisation of the tank, not just when filling, this means the fuel pump has a constant head/pressure, so we don't need a lift pump in the tank as most vehicles have these days, a simple but elegantly crude solution to carrying fuel in sealed container without open venting to atmosphere

[937carrera]

, a simple but elegantly crude solution to carrying fuel in sealed container without open venting to atmosphere

or venting into the intake (directly or indirectly), which is what most cars have.

[pkrboo]

because of the shape of the tank when the vehicle is going up a hill the fuel moves to the back of the tank and vice versa, and side to side the same, the breathers allow the vapour in the tank to balance regardless of angle and prevent pressurisation of the tank, not just when filling, this means the fuel pump has a constant head/pressure, so we don't need a lift pump in the tank as most vehicles have these days, a simple but elegantly crude solution to carrying fuel in sealed container without open venting to atmosphere

How does a syncro tank work?

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[Aidan]

Syncro has bunch of breather pipes on top of the tank balancing between the two roll over valves but does ultimately vent to atmosphere behind the filler cap , Syncro tank isn't U shaped, very late versions for countries with stricter emissions have slightly more convoluted set up with charcoal canister

[pkrboo]

Syncro has bunch of breather pipes on top of the tank balancing between the two roll over valves but does ultimately vent to atmosphere behind the filler cap , Syncro tank isn't U shaped, very late versions for countries with stricter emissions have slightly more convoluted set up with charcoal canister

Ahh yes, thats why the pipes on top are so long

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[fendad]

By the shape of the tank , when you tried to fill to the top air ( vapours) would be pushed to the top of the high points of the tank , airlocks , and with out the breathers and expansion tanks the filling would stop before full .
Like wise when the ambient temperature rose there would be nowhere for the expanding fuel and vapours to go to . The filler neck is only in one side in the tank to allow that breather to tank the expansion From the other side high point


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Are the 2 expansion tanks connected directly to each other?
The pipe from the tops of both of mine are just loose (see photo)
Should the 2 pipes join with a connector ruining across the top of the tank?