Thread: How do I install 2 fuel tanks in a Series 3?

A bit more info needed - where is the "Main tank" in the rear or under the drivers seat?

There are 3 types of series tanks:
Rear tanks (usually only fitted to station wagons and late model S3s)
16 Gallon (long range) underseat tanks
10 Gallon (shorter range) underseat tanks

Note that underseat tanks are the same from LHS-RHS.

If you want to fit a tanks - 1st check if the front outrigger the tank needs to bolt to is fitted (there is a different position for this if it is a 16 or 10 gal tank). If it is not fitted, then you will need to get one and weld it to the chassis. Chances are if it is not fitted, you will also need to cut holes for the filler and breather in the bulkhead behind the seat box, and also cut a hole for a filler and rivet one in to the side panel.

As for the changeover switch - a panel-mount teflon-seat ball valve will work fine, and shouldn't cost more than $30.

I have a standard 10 Gal tank under the drivers seat, and a 10 Gal army tank with brass dip stick. I also have the filler. I know that I will need to cut a hole.

My main problem is how to make the petrol from one tank to the other. How does the dall valve work, is it a pump? The rest is ok to fit.

You don't take the fuel from one tank to the other, you just install a 3-way ball valve - like this

LHS TANK
|
|
|
| (ball valve)
X-------------Fuel PUMP-------ENGINE
|
|
|
|
RHS TANK

So the ball valve just decides which tank you suck from. A toggle switch to change between fuel senders helps too!