The ¼ tank failure mode is almost always from the o-ring leaking going down to the siphon jets. It just makes the siphons weaker so they need doin some amount of fuel at the bottom of the tank to function.

If they didn’t work at all, the fuel would all stay on the left tank until it can flood over to the right. That happens at about 27L on E53, not sure when in E36.

The positive confirmation on e53 is the right tank will read a constant 1.4L of fuel steady state driving once you get below about 27L but at ≈ ¼ tank the 1.4L will start dropping to zero. You only have a few minutes/miles if that happens. When right tank reads zero there’s about 1 gallon left but your can’t drive 15-20 miles as the fuel pump will be pushing fuel to the left tank.


–awr–

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