Thread: Twin fuel tanks - a different approach

Interesting, but unnecessarily technical.. The 2" connector need only be 1" I/D.. Fill tank is RH tank with an outlet at the bottom rear corner facing the left tank. Left tank has an inlet at its rear RH corner... but not at the bottom. This one needs to be half way up, with a 90 deg bend pointing down and with a male thread. On this thread, will be fitted a brass 1" I/D one way valve in the upright position... (Mitre 10 carry these. You need the swing paddle type, not the spring ball type). The LH tank becomes the suction/run tank with fuel pick ups etc. The original gauge goes in the left tank and this is the running tank. If you choose to, you can fit an additional gauge in the original tank. You then have one filler, and fill normally. Both tanks fill together. As fuel is used the vehicle motion forces fuel from the RH tank to the LH tank keeping it full and slowly draining the RH tank. When the fuel gauge eventually moves off full, it means that the RH tank is dry and you have only what's left in the LH tank to use. The two tank breathers need to be linked together to the original filler neck, and need to be at least 3/4" ID. This is the system I run on the 101, and on the previous 101. Its simple, faultless and just works. Have a look next weekend and I'll show u the bits needed!

I think I get the gist of it - but I'll need a bit more of an explanation over a beer or two would be good.

When you build the system suggested by Sitec take lots of pics so I can copy it too

I will - I'm finally getting to see Sitec's 101 since it left Melboure - not so long ago in the grand scheme of things, but back then it had a not so healthy V8, leaking swivel seals and needed lots of TLC.

Simon has done that and more - I'm itching to get a real long look at it and go for a spin - I'll see if that changes my mind about which way I'm going to go with the engine....

Originally Posted by bacicat

So,I’ve been thinking hard about how to build a twin tank fuel system for the Series that is a bit easier to use and a bit more modern in its function than changing a tap over when you start to run out of fuel, kicking the passenger out to fill the second tank and not knowing how much fuel is in the passenger tank.

Well,I have come up with a solution that is a little more elegant than that. My research for parts and information shows this should all work (famous last words) and all the parts are currently on their way so I can test this all out.

Some of you may think the setup I’m about to describe as overly complicated to run a carby engine, or what should be on a Series vehicle, but the complexity doesn’tworry me, and eventually the engine will be fuel injected, so this all works towards that goal as well.

So,as best as I can describe it, this is what I’m going to try and make work…

There will be an identical fill point on the outside of the vehicle on the passenger side of the car, and a 2” balance tube put in at the top back of the tanks –this will sit under the seat box nicely and not be in the way. The upshot of this is that the car can be filled from either side and it will fill both tanks. As per the drawing below, fuel line 1 runs out of the factory tank, through an electric fuel pump, then through a venturi pump with the fuel being deposited in the swirl pot through line 3. The venturi pump will draw fuel from the extra tank, through line 2 and into the swirl pot through line 3. The fuel from the swirl pot is returned to the main tank through line 4. Excess fuel then drains back through the balance tube to the second tank.

The engine will draw its fuel from the swirl pot through its own pump. When I put the EFI on it, I can add one more line from the engine back to the swirl pot and I’m done.

In this way, the main tank will stay full until the second tank is empty, then the main tank will drain down. The drawback of this is that the fuel gauge will show full until half the fuel is gone… A minor problem I can live with for the time being and something I will look at later.

The hardest part with getting this to work was finding a suitable venturi pump, butI’ve got one on my way that in theory should work – I’ve still got to test actual fuel rates when I get it, but it only needs to draw marginally more from the second tank than what the engine is consuming.

The filler caps will be made so that no fuel can spill out of each side if the vehicle is on a decent angle with full tanks.

So, soon I will be modifying both tanks for the extra bits I need on them and dummying the whole system up for a test.

I know this won’t be everyone’s cup of tea, but there are several things on this build that will be out of left field. Wait until I start the wiring….

That's basically the same setup in a Landy I bought recently. I will upload some photos when I get home. They both fill from the same port on the drivers side..

Wolf

• So are you going to have a shut-off in the pipe between the two tanks? Have you considered what will happen when traversing a side slope? (the fuel will flow along the balance pipe, overfilling the lower tank and start splashing out the lower filler or any other leak point.)
• Many dual tank systems, use a single filler. You can run a pipe from inside the filler cap down to the tank on the tank on the other side (or at the rear). This pipe will be less likely to transfer fuel to the lower tank on a slide slope because of the height difference.
• As has been said before, keep it simple, less points of failure. There is nothing more simple than a mechanical tap and a switch to change over guage.
• The other option when you have a full flow system is to use a fuel transfer pump and transfer fuel from the reserve/secondary tank when the main tank gets low.

Yes, considered the fuel leakage on steep side angles, the fuel caps will be sealed and a breather pipe run higher than the steepest angle possible - up he back of the tray - like we do on our gensets that go on tilt trays to avoid spillage. Unless it's on its roof, nothing will leak.

Simple is good, I'll grant you that, but this project is going to have a few things a bit out of the ordinary. I'll be having a look at Sitec's system on the weekend as that sounds like it does the same thing, but is simpler in design.

Hi bacicat, I bought a series 2a 1969 109 6cyl van a couple years ago. it was fitted with factory twin tanks, (pressed metal type) both 16 gallons each. it had a switch on the dash that had the legend fuel pump 1 and fuel pump 2,. it was fitted with a weird looking double electric su type fuel pump above the handbrake area next to the right tank. it was plumbed with a pipe from left tank to the front part of pump and same from right tank to the rear of the pump, which had a single outlet up to the carby. I have a couple pics on my phone im trying to upload to my laptop and when I can i'll post them. the left tank was disconnected coz it was stuffed and the pipe was looped to the pump somehow. the switch was a DPDT. and the fuel gauges switched with the fuel pump, so, when on left tank, fuel gauge showed left tank's level and vice versa. wish I still had it coz I got twin tanks in my 67 landy now with a tap and switch for gauges. I was thinking of using gas lock off solenoids and an electric pump on mine but couldn't be bothered as simple is usually best, IMHO

Cheers Rod