self draining patrol sub-tank

Sorry locallaw don't think I can help. My 2000 Patrol will run out of full but won't drain the sub unless I hit the sub tank button on the dash. It will then empty the sub into the main. If you turn off the ignition before it's finished then you have to hit the button again when you start the engine again.

Cheers

Nomad

Might be something to do with the venting of the tanks.

Why does it bother you?

Locallaw
This problem is standard practice on my GQ when I fitted ARB main tank and aux.
Fill them both and it draws down the aux then the main, no switches pumps or anything else mechanical. I know the GU is supposed to work with a transfer pump and the only thing I can think of would be that the breather hose to let air into your main tank must be partially blocked, therefore creating a restriction and making it draw from the aux tank. That is my thoughts.
Bigbear

Hi Locallaw,
As far as I know, the sub tank pump runs for a pre-determined time at startup on my 98 GU 4.2, is this what you are talking about?

With the GU 3.0 litre, the sub tank transfer pump operates for several seconds every time you restart the engine.
This is a design feature to ensure the pump does not gum up from non use.
The result of this is that over several days of intermitittant driving the sub tank becomes empty.
It is annoying but at least the fuel is always fresh and free from bugs.
Perhaps you system is the same,ask your Nissan dealer or ring tech line.
Regards

It does this so you don't run out fo fuel while the sub is still full, as above, runs for a pre-determined time each time the engine starts. Don't understand why this would be a fault? There to ensure fuel mixes and does not go "stale" by sitting in the sub for extended periods. You will find on long trips does not happen due to the reasons already listed. I think its a good system, use it to you're advantage
rolande

Locallaw.
The transfer pump on all Nissans have valves in them like a normal mechanical petrol pump, these valves alow fuel to flow from the auxilary tank to the main tank. The pump does not have to be switched on for this to happen because the motion of the vehicle is enough to force the valves open whenever you go around a corner. Some one started this myth about the pump being turned on by the computer on start up and the myth has become common belief. You will find almost pumps on auxilary tanks do the same even on models without a computor. Eric.

Locallow,
R.T.F.M. read page 1-23 of the owners handbook.This is normal. It stops fuel going stale by ensureing its mixed and used.

Thanks to everyone who replied.I received quiet a lot of different answers but I have a good idea what is happening now.
Thanks everyone
Martin(locallaw)