Diesel Dual tanks

**Lionelgee** · 7th April 2012, 07:52 AM

Hello All,

Has anyone any experience with diesel dual tanks? After not being able to find the second filling point or any taps to change in between tanks I found both today. Oh after the ute now named "Baldrick" stopped running. Apparently the fuel gauge is not accurate - go figure! After a while I found a lever which I reckon could be the tap to switch between tanks. There is also an On/Off toggle switch near the lever where up is "On" written in Red and Down is "Off" written in Black. So when the toggle switch is on and as soon as the ignition switch is turned to the "Charge" red light on the dash panel there are pump type sounds coming from behind the toggle switch. Now I am presuming this is a fuel pump that brings fuel circulating into the system - how long should I have this pump going for? As soon as the key is turned to the glow plug warming position or the ignition position the fuel pump sound stops.

How long should I have the pump working before shifting the ignition switch to warm the glow plugs or start the engine?

Also with the lever - when the black plastic covered main length of the lever is towards the driver's side could this mean it is drawing fuel from the driver's side tank and when the black handle part is turned around so it is facing the passenger side could this mean it is drawing fuel from the passenger side tank - or have I got this around the wrong way???

I hope every one is having a safe and Happy Easter.

Kind Regards
Lionel

**87County** · 7th April 2012, 08:29 AM

there are a few common methods for dual tank operation in a diesel with a lift pump on the engine...

does each tank have its own filler or is the filler common to both tanks?

do you know if the spill-back from the injection pump goes just to one tank?

what type of diesel engine is it (200 or 300tdi, 4bd1, td5 etc) ?

if, as you say, there is an electric pump sound when you switch it on, then it could just be a simple transfer top-up to the main - if so try switching it on for a few minutes and see if the fuel gauge shows a content increase.

**zulu Delta 534** · 7th April 2012, 12:17 PM

How are your tanks plumbed?
Do you have separate gauges for each tank?
Into which tank does your return line drain?
Sometimes dual tanks are plumbed so that all the action takes place out of the original tank (you cannot have a return line returning unused fuel to an already full tank!) and the second tank is simply a spare. In this case there would be a pump to transfer fuel to and from the spare tank and the one that is in use and draining. Also your gauge would only show the usable tank.
Another way is to plumb both tanks through a switch so that the lift pump will suck from whichever tank you have selected, but this is not such a straightforward switching device in that the return line should also be switched at the same time to return unused fuel to the tank that is currently in use.
Without seeing your setup I would be tempted to say that the pump you hear may well be a transfer pump from the main tank to and from the spare tank, the direction controlled by the under seat tap.
A tap such as the one you have pictured will select the side that the direction of the handle shows. That is, if the handle is to the drivers side, then that is the side of the tap that is open.
You are going to have to a bit of trial and error searching to see how your set up is set up.
When you next fill up, experiment by putting only a known amount in the main tank and checking what your gauge says.
I suspect that if you put 20 or so litres in your main tank then the gauge should reflect this. If you then turn your tap to the other side and turn on the pump and pump from this primary tank to the secondary tank, the gauge should register any change, and at least you will know (a) your gauge works, and (b) it only reads on the main tank.
Of course if you have only the one filling point then you must be relying on the transfer pump to transfer from that tank to the other (spare) which seems a weird way to do things.
I would suggest if there is only the one filler point that you modify this system so that the two tanks are joined with a pipe situated at the bottom of each tank that will transfer by gravity and apply a control isolating tap to this pipe. If you cannot control the transfer between the two tanks somehow, when the tanks are low and you are operating on uneven ground it would be very easy to suck up a belly full of air which in a diesel is most undesirable.
Hope this isn't too convoluted.
Regards
Glen

**Lionelgee** · 7th April 2012, 02:58 PM

Hello Zulu Delta 534,

I did find the second filling point and it was under the passenger side bucket seat.

I also worked out another purpose for the pump. It is a gift from God when one needs to prime the system again. I did not have to pump the manual priming pump at all. I just clicked the electric pump on and opened the left bleed screw until all the nasty air bubbles went away and it was a nice steady stream of diesel. Then on to number two bleed screw and did the same thing. Went back and turned the pump off and turned the ignition and after the pause for the glow plugs I turned the ignition and Baldrick roared back into life.

I would like to thank the 2nd last owner (maybe original owner?) before me, who installed that pump. I just sat on the mudguard undid the bleed screw with a socket and observed the flow of air bubbles until there were none left. I tightened the bleed screw up and hopped down. It took only a couple of minutes - no bark off the knuckles or blood spilt. No needing the hands of a midwife grafted onto the body of a contortionist. I would like to thank the previous owner who was an electrical engineer who had the foresight to install the pump.

Now that Baldrick is going again I will sort out the plumbing.

Thank you Zulu Delta for the information and I will now have a closer look at the finer points of the plumbing set up.

There are two fuel gauges - neither of which work and both tanks have 20 litres in them each. I figured if I cannot work out what the lever does straight off I will have both tanks equally full so I do not have to run out of fuel again.

Kind Regards
Lionel

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