Sub Tanks

[Dirty Driver]

Question for my more experienced colleagues out there in 'trolland'.

Can anyone tell me how I can stop the 10 second purge of fuel from the sub tank back into the main fuel tank upon start up in my 2000 series II GU wagon?

I find it really annoying when I fill the sub tank on the grounds it's there for reserve, only to have it ekked away every time I start the bus...

Any assistance or guidance that could be provided would be greatly appreciated.

Cheers

DD

[DX grunt]

I think we all share your pain, brother.

I put $20 in mine the other day and it's nearly gone allready.

Diesel in my town is $161.2 at the mo. Disgusting!!!!~!!

[Maxhead]

My sub needle doesn't move at all, I can turn the truck on and off for a full main tank and hardly any disappears from the sub. I know they do prime a bit at start up but not that much...on mine anyway.

[BillsGU]

I agree with you Pat. The whole idea is to keep the pump turning over so the seals / whatever do not dry out / whatever. That way - when you really NEED the pump, you know it works. Gee DX - the fuel is not pumped overboard. It goes into your main tank and is not wasted. Just my two bobs worth.

[YNOT]

There's no point having a sub tank full of diesel for "just in case" if the fuels gone off from sitting unused in the tank for too long.

Tony

[Leighw85]

so im guessing thats very interesting??? lol

yeah my sub tank does not drop at all. I fill both my tanks up at the servo every time. When my main tank empties, my sub tank is still full

[teleman]

Yep, Mine needle hardly goes down as well. Mind you, when i fill up, Im the annoying guy who spends ages at the pump. I like to wait till the air bubbles have settled down and keep on filling. Get as much in there as possible. As a result, im now getting consistent 950 - 1050 kms per fill up.
Very happy :)

[robbo0001]

So what exactly is the function of the Sub tank? Is it an auto top-up feature for the main tank, or an emergency reserve that is solely selected by the dash switch, ONCE the main tank has reached a preset level?

Just filled the 2.8 from empty (both tanks) to full (both tanks) for the first time...took 114 litres of go-juice.
Have tried manually selecting the sub-tank, but the selector switch light extinguishes after aprox 10 seconds...so its back on the main tank?
Is there a auto "lock-out" (in tank float) that stops the sb-tank over-priming the main tank?

Sorry for the questions, just trying to work out the correct function of this system.
Cheers
Robbo

[YNOT]

GU's always drawer fuel from the main tank, you use the fuel in the sub tank by transfering to the main tank. If your main tank is still full the transfer pump will be shut off to stop the main tank over filling.

Tony

[robbo0001]

Sweet mate, thanks for the prompt answer..

So a "self-priming" transfer of fuel, as the first post from Dirty Driver, is a fault from standard?

Spent today listening for the auto pump transfer, after reading this yesterday...now I can concentrate on other noises :wink:

[YNOT]

The transfer pump is programmed to transfer a small amount of fuel at each start up to keep the fuel turning over. The main transfer of fuel has to be initiated by the driver through the sub tank switch.

Tony

[robbo0001]

Cheers again Tony...makes sense now.

[wheels]

Transfer from the subtank to the main tank will only work once your main tank is on 3/4 mark.

[Pete's GU3]

You can actually see the fuel going over if you open both fuel caps , it pumps it from near the top of the caps ....

[the evil twin]

The transfer pump is programmed to transfer a small amount of fuel at each start up to keep the fuel turning over. The main transfer of fuel has to be initiated by the driver through the sub tank switch.

Tony

Don't disagree that it turns over the fuel as well but IMHO the reason Mr Nissan did it the way he has is as a self test of the system on start up.

Every time you start, IF there is fuel in the sub the transfer "test" happens and if there is a fault the Sub Tank Warning light comes on to tell you the fuel in the Sub is unavailable.
No fuel in the sub then no self test happens.
Fuel in the sub and no transfer = warning light
Fuel in the sub and transfer works = all good

The more starts you do the quicker the fuel gets transferred but at around 1 and 1/2 litres per minute it takes a lot of starts to transfer a noriceable amount.

Mr Nissan used the same logic in his Cruise Control safety lock self test... after each start the Cruise won't engage unless you have applied the brakes at least once.

[Pete's GU3]

same thing has happened with mine again , i have a full sub tank and the warning light has come on , the main tank is 1/4 full but still no fuel will be pumped across until it gets reset ..

[razzar]

i have the petrol model and I do not notice the sub tank being used at each start up. The sub tank is always full when I fill the main tank at the fuel station and have not uesed the sub.

[Shaunous]

There's no point having a sub tank full of diesel for "just in case" if the fuels gone off from sitting unused in the tank for too long.

Tony


In my 10years experience of heavy diesel/earthmoving mechanic's i have never seen diesel go off, or heard of it going off. I have come across off petrol and know it deffinately goes off. Not saying diesel doesn't, as it probably does, but maybe after a number of years.

My sub tank does the same thing, i'd rather my sub tank full and not keep getting lower and lower everytime i start up.