That is basically correct. When there is a little more maybe up to 10 L the recirculation of fuel will help a little bit but basically until the low light comes on the pump will get no increase in cooling. Again a brilliant design needing the bare minimum of fuel to run the engine and to cool the pump.

When the fuel is more than 5L, the excess goes in circles.

The fuel pump sends fuel to the filler/regulator, what is not used goes back to left side, that collects fuel from the left side and dumps into the right side which spills like a waterfall back to the left side. Any time the left side of the tank is cooler than the right side, some chilling will occur but since the turnover is limited and slow, it's not a significant factor so the reality is the fuel pump will be completely submerged by fuel that is cooled by conduction to the very large plastic fuel tank, you will have effective fuel pump cooling down to 0.0 on the gauge.

Also, it's important for the reasons above to test the siphon system periodically so you know the pump isn't worn and the seals are working.

Test Six should report about 1.3-1.4L right side on level ground driving steady state. If you learn what your particular car shows you can verify the system is working. If the right side ever drops below your baseline most likely the pump is worn out but also a good chance the stupid no o-ring seam on the siphon jet has failed. That can be fixed for free don't replace with the identical flawed design.

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