AWR-fix: e53 Fuel pump / siphon pump details

[andrewwynn]

Saga is over. Definitive results!

I siphoned out the gas in the reserve tank and weighed it to the gram.

The gauge read 0.7 L but there was 4.3L in the tank or 3.6L left at 0.0L or 0 miles dte.

That is just shy of a gallon. I would expect about 15 miles of range before the pump may have problems going around corners etc. (after hitting 0 miles to go).

Summary: I drove my car down to 1 mile dte and there was just about 1 gallon in the reserve tank. I am far more confident in driving down to single digits.

I got down to about 5 miles to empty before the surge tank was no longer spilling into the main tank.

In other words until you are down to FIVE MILES to empty there is no functional difference in the fuel supply system.

The tank ended up being a little smaller than I thought: I was guessing 6-8L and it turns out the reserve tank is about exactly 5.0L.

My right gauge said their was 0.7L when there was 4.3L. The gauge was dialed in to not include the last 3.6L of gas in my case which is perfect: consider that gas like the last bit of stick deodorant, not meant for consumption just to keep the pump submerged down to 0 miles to empty at any angle of road (or un-road).

So "now we know". The surge / reserve tank on the e53 is 5L. The car is absolutely unaware that it has a bigger tank once there is less than about 35L of gas according to the gauges as any more than 5L in the reserve tank will simply spill over to the main tank on the left side.

The calibration on my wife's car with the new pump shows 1.4L but every car would likely be different. That said, simple math will tell you what your true reserve is.

The computer will estimate 0 miles to go at 8L for 6 cylinder and 10L for 8 cylinder models.