# Explain the Fuel System- Tank, Expansion tank, ventilation, charcoal cannister, etc.



## BigWalmac (Jun 22, 2009)

I have a fun chalenge for someone bored on a Tuesday...

My wife's 01 X5 is in the shop. Smell of gas that is out of the ordinary. Separately, oftentimes while filling the X5 will "pop" and act as if the tank is full, even though it is only 1/2 full. Yet other times the tank will fill and overflow into the filling well and run out in front of the rear tire (overflow)??

In any event, dealer and an indy shop are unsure on how to fix this. 

Can someone please explain to to me all the workings of the Fuel tank/fuel filling/fuel supply/ventilation system?

Attached is what I can find of the diagramn, but I cant make heads or tails of how all the parts play together and what tehy do...

Alot more complex than my initial thoughts of line into tank to fill line out of tank to engine...

Thansk guys.


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## chrisn7 (Oct 15, 2011)

Not familiar with the X5, but E38 owners also know about the fuel tank 'bong' which arises because of partial collapse of the tank as fuel is consumed, then suddenly released. This usually results in fuel tank leakage from splitting. I have seen and participated in other discussions on this subject, but no-one has yet been able to identify the exact cause. Because of this some UK owners, including me, have drilled a small hole in the tank cap to provde venting-not ideal, but it saves the tank until the correct solution is found. This may not be for you though due to emissions.


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