Twin Tank Setups

[Bailes1992]

Our Classic Mini comes with a ~35litre fuel tank as standard giving us a range ~250miles this is mounted on the left hand side of the boot.

The early Cooper S models had the option of a 2nd fuel tank mounted on the right hand side of the boot giving an additional ~25litres. These tanks are still available.

While I have our Mini in bits I think it would be a nice modification to install the 2nd tank and give us a better range.

The Mini is fuel injected so has an in tank pump, return and EVAP going to the left hand tank.

My plan would be to run a vent between the top of both tanks, probably tee'd into the EVAP line. And another line between the bottom of each tank. Both tanks are at the same height so fuel can run freely between them to allow them to maintain the same level and I wouldn't need any extra senders or pumps.

My question, with the 2nd tank there would be a filler on either side of the car. How big would I have to make the balance pipe so both tanks would fill from whichever side you decided to fill up from?

 

[mk378]

What was the factory plumbing for two tanks? Can you get the parts to duplicate that?

Lines connected to the bottom are not a good idea since they will leak uncontrollably if damaged in a crash. Lines from the top can't spill fuel after the pump stops.

 

[BMWTurboDzl]

I'm surprised that there isn't a kit for the Classic Mini community vs you having to figure it out yourself. Have you found photos of schematics of the factory option?

 

[Bailes1992]

There is kits available. Looks like a 5/16ths pipe between the tanks. I just can't see that being big enough to enable the filling of both tanks from one side.

 

[mk378]

Big trucks have the bottom of the tanks connected with a relatively small hose as described. The tanks do have to be filled separately. Truck stops have an extra hose for the tank on the other side of the truck, the same pump feeds both hoses.

 

[BMWTurboDzl]

There is kits available. Looks like a 5/16ths pipe between the tanks. I just can't see that being big enough to enable the filling of both tanks from one side.

I would go with the kit under the assumption that if there were a better way someone would've figured it out by now.

 

[earlyre]

 

[meep]

Subaru had a “saddle tank” design for a few years, idk if they still do. The design used was always using a bornulli pump fed by the fuel pump to shift fuel from one side of the saddle to the other, and that “other” side is the side that then fed the engine. Might be something worth gleaning ideas from.

 

[Surestick]

Subaru had a “saddle tank” design for a few years, idk if they still do. The design used was always using a bornulli pump fed by the fuel pump to shift fuel from one side of the saddle to the other, and that “other” side is the side that then fed the engine. Might be something worth gleaning ideas from.

*Bernoulli*
The fuel system is a return system (the excess fuel the fuel pump supplies is returned to the tank by the fuel pressure regulator). This fuel was put through a venturi creating low pressure that was used to pull fuel from the side of the tank that didn't have the fuel pick-up.

This doesn't solve the OP's filling issue though as the saddle tank only becomes two tanks once the fuel level drops below the top of the saddle so filling isn't an issue.