You said you added 9.6g but was that all that fit to fill it full? (That was my understanding).

If so you will be way past Flood stage and siphon jet doesn't come into play.

I never measured how much fuel just circulates vs. goes to the engine but at idle I'm confident a lot more fuel goes back to the left tank vs. consumed by the engine.

The tank has two lobes, the left is much larger and has no electric pump, the right is much smaller and it's where the electric pump is located.

The two lobes are connected at the top with a hump in the middle that when enough fuel is consumed they become separated. This happens at ≈ 27L total fuel according to the gauge.

At this point there will be about 5L of fuel in the right lobe, 3.6 which does not register on the gauge and 1.4L that does. (the 1.4 can be different on each car and should be learned by getting fuel lower than 1/4 tank and using test six to read the value).

When the tank has less than 27L, the fuel supply uses the excess gas returning from the fuel pressure regulator to generate a vacuum at two separate siphon jets at the front and back of the left tank lobe.

(2 of the three hoses that go from left to right: the third being to a pressure relief valve in case there's a blockage in the siphon system or any other failure that would put too much pressure on the system)

When working properly the siphons will pull fuel from the left to right continuously but it only matters when less than 27L.

At that point and less, the siphon jets will keep the right lobe overflowing the center hump and the right side will stay filled to 5L until the left side is bone dry.

When the siphon jet fails, it will fall to put enough fuel to the right and the right side will go empty since the pump pushes fuel from right to left but the siphon stops pushing the fuel back to the right.

When people "in the know" realize their car is stumbling but happens to be near 1/4 tank, they will take a hard left turn to slosh some fuel over to the right and make haste to a gas station.

If you happened to be near 1/4 tank, hard turns can easily cause engine performance oddities as fuel gets shot out of the tank by the pump and tossed back in by a hard left turn.

If the fuel level is ≥ 27L the siphon is removed from the equation.

Any questions?


–awr–

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)