Sub Tanks

[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.