323 Fuel system ?

I have searched this forum & found no acceptable answer or (more likely) I did not recognize it

Let me start by wanting to know what the tank in the boot does
Is this just to increase capacity or ?
And how do you fill it, as the filler is about in line with the top part of the tank ? Or is that German ingenuity in keeing air-space in the tank ? But for that you have the expansion tank in the right of the trunk

I see it has a own Fuel level sender unit coupled to the 2 in the tank. Since I was not bothered in tracing the wires, I must assume that it runs in series with the 2 in the tank, that are probably wired in parralel

Anybody KNOWS what is going on here, or is that a reason that the Germans lost 2 WW's & 1 World Cup

Then what must the fuel flow be, from the Low volume pump in the main tank under the seat ?
Please do not tell me to hook up a low pressure fuel gauge & when thrashing it on the Dyno it must still deliver fuel pressure

This is driving me

On a seperate note, I see this E30 has no oil cooler. Where do I get the adapter from ?
BMW probably has an adapter with a Thermostat inside, that only alows the oil to be cooled over 100 C or so

The Aux tank gave you just that Increased Capacity. The factory did them as did Hartge and Alpina in different flavors.

They work off of gravity. The Aux is filled first flowing down to the main.

The fill line is different from a standard E30 It's a two line system. I don't have time to photo it but try www.realoem.co and review the fuel systems there.

Next question:

Why do you need or want this? Do you need an extra 25L for Autobahn cruising? This is what they were designed for, back when fuel was free and the West German Autobahn's were free of Lorries and Motorhomes from the various surrounding countries. The fact that very limited portions of the old UNrestricted section just don't exist anymore.

i am thankful that each time I fly into the Eifel region I can blast down the Autobahn to das Nurburg ring for a fun day.

Edit:Alpina tanks, I have one and two EU extended range tanks.