7 replies to this topic

[Chewy]

Hey

I have got got my hands on a ali fuel tank for my mini that has a got a 3.5 gallon rubber bag in side it has no leaks how could i rig this up so when i fill the proper mini tank it fills the ali tank aswell any susgestion

I was goin to have the ali tank as a reserve tank on a y piece that goes in place of the mini fuel line with a tap in so when the mini tank is empty turn the tap and then use the fuel in the ali tank would this be ok

[dklawson]

It sounds like you have a fuel cell, not just a fuel tank. If you don't have and use the proper filler neck for the second tank you will not have good results. There are several things to keep in mind.

1) The second tank has to be vented. If you don't, no cleverness will get fuel into the tank. The second tank would have trapped air in it so the fuel would never enter it from the first tank.
2) The second tank must have its vent (and/or filler neck) at the same elevation as the stock Mini tank. If you DON'T do this, when the fuel level in the stock tank is high or full, it will siphon into and out of the second tank's vent.
3) Even if you do insure the second tank is at the correct elevation and has proper venting, it will fill VERY slowly through the "Y" or "T" piece. There is no way around this. Even if you use the biggest reasonable hose you can find... it won't change the fact that the stock Mini tank with the filler neck uses a 1/4" diameter nipple on its discharge port. The size of that port will control the flow of fuel into the second tank.

In summary, mount the second tank at the same height as the stock tank. Make sure the second tank is vented. Provide some method to fill the second tank directly... not through its discharge port via the stock tank. The "Y" or "T" piece along with fuel hose will work but only if you adhere to the other steps.

Edited by dklawson, 18 November 2007 - 04:36 PM.

[Ethel]

Wouldn't there be an issue if one tank emptied first, as might happen if the bottom of one tank was higher?

[Chewy]

The ali tank has its own filler neck i might plumb it it in a reserve tank on a tap in the boot

[dklawson]

Wouldn't there be an issue if one tank emptied first, as might happen if the bottom of one tank was higher?

Since the tanks are bound to be different heights it's almost a certainty that one tank (probably the aftermarket one) will go dry first. Since the tanks have to be joined together with the "Y" or "T" piece this is not a problem. The fuel pump isn't going to selectively suck air out of the dry tank, they are not plumbed individually to the pump.

For reference, keep in mind that the Cooper-S with twin tanks did nothing more than join the LH and RH tanks using a crossover pipe. The two tanks thus joined fed the fuel pump with a single "T" line through the boot floor. The biggest problem I have ever heard of regarding this is overfilling the tanks and immediately parking the car on a hill such that the excess gas flowed to the lower tank and either out its vent or filler neck.

Edited by dklawson, 18 November 2007 - 08:08 PM.

[Chewy]

Ok

What if i plumbed the ali tank with a tap to one of the outlets on the y piece turn the tap off
then the fuel in the mini tank will be used first then i turn the tap on then the fuel from the ali tank will be drained then will this work

[dklawson]

Yes, using a manual selector valve would work. It's my understanding that in the 1950s the VW Beetle operated like that. When the engine would start to cough and sputter you'd get out and turn the valve to draw fuel from the auxiliary tank.

[Chewy]

Thanks


All plumbed in and no leaks i am gonna see how many miles i can get out of both tanks