55l to 63l fuel tank swap

[Cook318IS]

I'm expecting that the extra few litres will come in useful when I get my new engine in, so how much of a ballache is it to upgrade to the bigger fuel tank? I know i'll need a fuel gauge to match the bigger tank, but is there a point in the loom where you can plug in the wiring for the bigger tank setup to accommodate the twin senders and the two pumps (the bigger tanks use 2 pumps right?)

Cheers!

(Car in question is a 2 door facelift 316i)

[maggspower]

The pump wiring will fit, there is only one pump though.

The senders need to be wired up in series so the the resistors in them can control the gauge correctly, and yes that gauge needs to be one from a car that came with a 63L tank.

The lines are a little different too.

[Brianmoooore]

(the bigger tanks use 2 pumps right?)

Wrong! Just the one pump. Existing one (and level sender) can be used, but the fuel return pipe on it needs to be blanked off. Easiest way is a short length of hose and something like a bolt.
Best way to connect the LH fuel sender is to run a length of twin cable across the top of the tank, from one sender to the other.
Connect the wires at the LH side to the sender, and at the RH side, cut the green/brown a couple of inches from the plug, solder the two cut ends to the two wires from the LH side, and insulate with heat shrink sleeving. Doesn't matter which way around you connect the wires.
Last thing is to cut back the return pipe from the front of the car to the now blanked off pipe on the fuel pump, and connect it to the stub pipe on the front LH side of the new tank.

[Cook318IS]

Ideal, cheers gents! I'm sure it'll make more sense when I can get a tank in my hands! It'll be a while off yet I expect. While there is no carpet or dash I think i'll prep for running an external pump for the swirl pot and run a cable in ready to replace the 1.5mm from the fuse box like the earlier 2 pump models after finding some drawings online!

Thanks again!