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Originally Posted by Crowz;
As in what does it have that makes it special for offroading angles and such?
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The little "bump" on the bottom of the tank is where the fuel pump resides. The pump is so low in the little bump that with 5L of gas the pump will be completely submerged at a 30° nose up or nose down attitude. (or left or right but I wouldn't attempt that one I don't know at what angle the x5 will tip but I've had mine at 37° down 12° list before and it was awesome.
The design is great! I couldn't start my Ford explorer with 1/4 tank of gas when parked in an angle driveway and that was only maybe 8° angle. I had to put in neutral, coast to the road then when close to horizontal the car will start what a moronic design for supposedly an off road vehicle.
The diagram you showed is one of the hundreds of incorrect resources I mentioned when researching the fuel system of the x5.
100% of the existing resources referenced similar designs implying or explicitly declaring that the x5 fuel pump had two equal lobes which can not be more innacurate!
If you break the x5 tank into three virtual tanks it makes more sense:
Tank A is used first, holds about 60L
Tank B holds about 28L and holds the spill over from tank C
Tank C holds 5L and is where ALL the fuel is actually pumped.
When tank A is empty, tank B continually pours fuel into C to the point of overflow to keep it completely filled to 5L up until tank B is empty. This keeps the pump submerged even at extreme angles and down to 0.0 gallons remaining since there is almost 4L more in the tank than reported by the instruments.
It's an absolutely brilliant system but leads to some confusion during trouble shooting that will have people draw the wrong conclusions such as "keeping more than 1/4 tank will help something" or "a defect in the siphon jet will wear out the electric pump" neither of which applies to an x5 .
(The fuel pump is fully submerged by recirculating fuel down to 1/18th of a tank well below the low fuel light)
(In the EXTREME rare case of a siphon jet failure you will fuel starve having run for no more than ten or 15 miles with the pump not submerged it will not likely cause any significant harm unless you follow the "fill at 1/4 tank rule in which case you can cause damage by running the pump uncovered without realizing it because once below 1/3 tank the ONLY thing keeping the pump covered is the siphon jet).
These are just facts based on research and first hand measurements and tests (and a few mouthfuls of 93 octane).
There is no more accurate resource for the e53 fuel pump online. (Than mine). My digrams are based on my measurements and photos of an actual e53 tank I took apart not supposition upon speculation upon myth based on 1950s gas without ethanol. It's cold hard facts.