Help in understanding my dual tank setup

G'day

I've bought a "new" GQ a while ago and I find it a bit difficult to work out how the dual tank setup works. I can't ask the previous owner as I bought it from a dealer who bought it from a middle man who bought it from another dealer. :1087: There's nada documentation about it.

My mechanic had a quick look and says there's my standard 90l tank and a 75l sub-tank. There's only one filler. There are two hoses going from that filler to the tanks. We figured out that there's a switch (on/off) which starts a pump in the sub-tank. There's also a light which comes on when that pump is going. At that point all seemed clear: once I can't get any more fuel in I've 165l with both tanks filled. I drive on my main tank and when the fuel light comes on I activate the pump. There should now be enough space in the main tank to empty my sub-tank. That's the theory.

In practice I filled up twice so far. First time after the fuel light was on for maybe 30km I got 82l in (gauge showed full afterwards). I didn't pump fuel over back then as I didn't yet know how the whole setup works.
The second time I filled up I got 95l in. Now that's more than the main tank so I reckon something must have gone in the sub-tank. In fact I assumed that both tanks had to be full at this stage as I didn't get any more fuel in.
Now that I tested the fuel pump with an half empty main tank it first seemed to pump for maybe 30 seconds (light is on and I can hear it work). Then it started to sound different and the light started flashing.

What's going on here? If my sub-tank is full why does it not pump it over?
If my sub tank was almost empty then how do I fill it??

Any ideas anyone?

Yendor or Growler may be who you seek

Would definitely need Growler or Yendor or someone rather than me..lol...But I'll have a guess.

You would most likely have a T piece half way down your main filler neck which would go into your aux tank, when main tank is full it would start to fill aux tank. Not an ideal set up but works.

Do you get a lot of splash back when filling up with fuel?

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Now that I tested the fuel pump with an half empty main tank it first seemed
to pump for maybe 30 seconds (light is on and I can hear it work). Then it
started to sound different and the light started flashing.

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To me that sounds like the aux tank running dry or a blockage in the pump/lines and the light flashing is a sensor alarm notifying you.

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If my sub-tank is full why does it not pump it over?

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If your 100% sure the sub tank was full then someone else needs to help here but from what you described sounds like the pump running dry.

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If my sub tank was almost empty then how do I fill it??

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As above, they normally fill when the main is full and the overflow goes into the aux through the T piece on the main neck. They can also be plumbed to get similar fuel at the same time when filling too.

Hopefully some more solid advice will come soon...lol

NFI sorry mate I've just got one small shitty tank

Boo hoo last time I nominate you, geeesh

Thanks AB. Looks like I need to try and fill up again.
I do get some splash. In some stations I need to turn the nozzle so that it doesn't stop all the time.

It really is a bit of a weird setup if it only has a T-piece. You can always only guess how much is left in your main tank in case you don't want to fill the aux tank as well. And to make sure they're both full you need to overfill I reckon.
Makes you wonder why not just put 2 fillers and two gauges in and have a switch to go from one to the other. $$ I guess.

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Originally Posted by Flo-w

Thanks AB. Looks like I need to try and fill up again.
I do get some splash. In some stations I need to turn the nozzle so that it doesn't stop all the time.

It really is a bit of a weird setup if it only has a T-piece. You can always only guess how much is left in your main tank in case you don't want to fill the aux tank as well. And to make sure they're both full you need to overfill I reckon.
Makes you wonder why not just put 2 fillers and two gauges in and have a switch to go from one to the other. $$ I guess.

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The proper dual necks are expensive that's probably why the bloke just tapped in to the main.

I'm currently putting an aux in mine and just spent over 100 on this puppy but I think it's worth it.

If your keen in getting one then click on the parts link at the top of the page and you should find one at a Patrolapart.

Attachment 37974

I wonder if they have grabbed a gu setup as they pump a little Fuel over each start up to prime / check the pump.
Could be your usage issue.

I think the is only one way to check your setup, start chasing fuel lines and and wiring..
Could be a cheap dual valve setup or an expensive 6 port valve..
You'll need to find out to understand it..

OK, tried again. The fuel gauge read half full (on a 90l tank) and my GF got 77l in before she got tired of it. That tells me that some of it went into the sub tank.
It looks like the fuel pump/line is blocked though as the pump makes a very tired noise and the red light keeps flashing.

Looks like I drive up to 75l of dead fuel around now. :( No time to get it fixed before Xmas. At least I won't need it in the high country as much as elsewhere.

Yep when you get a chance get underneath first and check the lines.

You should also have a filter before the transfer pump so check that first. Could be definitely blocked.

If the pump noise goes from loud knocking to a softer tap tap it is just priming. A few things for you to check below.
Is it your low fuel light that is blinking ?
Could it be the fuel from aux tank making float bounce ?
What port on main tank is pump outlet hose attached to?
Is the fuel sender on aux tank wired up?

Where are you located mate. I'd be keen to have a look and try work it out for you. I just wanna see how it's setup for my own when time comes to lol

Another question?
Does the pump switch have 3 positions?
Pump on
Main tank gauge
Aux tank gaugeAttachment 38142

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Originally Posted by liftlid

Another question?
Does the pump switch have 3 positions?

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Only 2 positions: on / off and a light which can be either on, off or blinking. It's off when the switch is off, it's on or blinking when the switch is on.

It's not a low fuel light that's blinking as there should be at least 30l in that aux tank now.
I don't think there's a fuel sensor on aux tank as I don't have a fuel gauge for aux tank.
I'll have to crawl underneath...

@ liftlid that's a duel fuel switch by the look of it, for switching from petrol to gas
It will have 3 positions as you need to run petrol dry before using gas otherwise it will dual fuel and run like a dog

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Originally Posted by threedogs

@ liftlid that's a duel fuel switch by the look of it, for switching from petrol to gas
It will have 3 positions as you need to run petrol dry before using gas otherwise it will dual fuel and run like a dog

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My picture was of a my diesel change over switch, g = gauge(aux tank)
Centre is main tank gauge, pump is to turn pump on to pump from aux to main tanks

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Originally Posted by Flo-w

Only 2 positions: on / off and a light which can be either on, off or blinking. It's off when the switch is off, it's on or blinking when the switch is on.

It's not a low fuel light that's blinking as there should be at least 30l in that aux tank now.
I don't think there's a fuel sensor on aux tank as I don't have a fuel gauge for aux tank.
I'll have to crawl underneath...

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Assuming that the blinking light is on the switch and not the low fuel light on the dash I wonder if the light starts blinking when the pump has pressure? If so you might find a pressure switch somewhere.
Another far fetched idea is that the pump is faulty and the circuit is fed through a circuit breaker which is tripping and re setting causing the light to start blinking, long shot but if the pump is not pumping ????
A standard tank holds 95 lt and you will have about 20 lt left when on empty.