Aux tank plumbing logic?

[Paulrotterdam]

I have an aftermarket 120L aux tank fitted by a PO but have never actually used it. We're currently in Iran and would love to profit from the ultra low fuel prices (€0,02/L) so looking to fill it up, but can't seem to figure out the plumbing.

The photo you see here is a T-piece fitted to the original fuel line with three taps.
- Line on the right comes from the aux tank.
- Line on the top comes from the normal tank.
- Line on the bottom goes to the engine.

The taps are currently in the 'normal tank mode'.

PO told me to close the top tap (normal tank) and open the right tap (aux tank)

With my logic it means that the fuel pump will draw fuel from the reserve tank to the engine and return fuel to the normal tank via the return fuel line thus filling the normal tank back up (minus the consumed fuel) .

Does this make sense? Is this a regular setup? How long do you guys think it will take to fill up the normal tank again (return flow rates?) Can you do this whilst driving or should you to this parked and with a running engine?

 

[Biggyniner]

Do you know if the two tanks vent lines are connected together? Something to check... You pose an interesting question however... If it's drawing from the Aux tank but vents/overflows to the main, in theory it could overflow? I mean it's unlikely I suppose, especially if you only use the aux tank when the primary is low...

 

[Paulrotterdam]

No the aux tank vents back to its own filler neck, so in theory it could overflow out of the normal tank I suppose

 

[roscoFJ73]

With my logic it means that the fuel pump will draw fuel from the reserve tank to the engine and return fuel to the normal tank via the return fuel line thus filling the normal tank back up (minus the consumed fuel)

No, to my thinking that's wrong. The fuel return should always return the fuel to the tank it came from.This is how Toyota does it

If it returns the fuel to another tank, it risks overflowing. Toyota diesels return as much as 3/4 of the fuel back to the tank.The excess fuel cools the inj pump.
Im surprised you went all that way before checking it.

 

[Paulrotterdam]

@roscoFJ73 thanks for explainig the way the system should have been installed, but seems I have a crude/simpler African solution under the car which mr toyota would probably disapprove of.

Does the plumbing I explained as I traced the lines make sense? Could it work if I switch back over in time when the normal tank is full?

 

[roscoFJ73]

Does the plumbing I explained as I traced the lines make sense? Could it work if I switch back over in time when the normal tank is full?

Its possible but home made aux tank fuel systems have a habit of unfathomable problems with fuel starvation ect. You can only try.
But i would try setting it up as Toyota do. Toyota setups have 4 valves I think an inlet and outlet for each tank.

Or , I would try using the aux to top up the main tank and pull the fuel from the main tank to the engine.

 

[Paulrotterdam]

Ok I tested the system and indeed it seems to transfer diesel from the aux to the original toyota tank via the return line from the diesel injection pump. So need to switch it back to the main tank before it starts to overflow!

 

[renago]

If you have a standard European 78 , these are NOT equipped with the dual tank , from mr toyota.
So the out fitter of the auxiliary tank simply found his way to feed the main , and only official tank via return pipe.
There are other ways to do this but , we/ should understand and respect what has been done on the car.
Unless , the outfitter didn't understand the mechanics of hydraulic ( sorry for the cacafonism) and did it his way ..


Bye Renago