How does the sub tank work

[Mc4by]

Can someone explain how the sub-tank works? I have a 2002 3.0 GU.
I press the sub-tank button and the light comes on. About 2 minutes later it goes off. Is this normal or do I need to get this sorted?
I have a near full main tank and wanted to run off the sub to make sure it was working fine.
The vehicle is new to me and is my first patrol so I have no idea what is supposed to happen.

[TPC]

The sub tank gets pumped into the main tank, if your main tank is full it will not pump into it.

[TimE]

Yep, on mine it won't pump until the main is at least 1/3 empty.

[Mc4by]

Thanks for the info TPC.
I thought it was a choice of which tank you could use and so I was going to run the sub tank down and go on to the main.
Strange thing about being a newbie....you look stupid but learn lots really fast.

[AB]

Thanks for the info TPC. I thought it was a choice of which tank you could use and so I was going to run the sub tank down and go on to the main. Strange thing about being a newbie....you look stupid but learn lots really fast.

Not stupid at all. You asked a question and now you know.

Everyone has to learn by asking questions.

[TimE]

.... and just to be clear, the sub tank pumps fuel into the main tank, fuel to the engine is only drawn from the main tank.

[Cuppa]

Not stupid at all. You asked a question and now you know.

Everyone has to learn by asking questions.

But what is stupid, & makes no logical sense (to me) is the Patrol’s sub tank operation. Why on earth was it designed to pump from one tank to another & then pump it out of the main tank (which sits at the rear of the chassis - at least it does on my ute). Is there an advantage to this method I’m not seeing? If in every day use one uses only the main tank then the weight of fuel is in the worst position. Toyota’s have a separate pump from each tank & a switch to allow the vehicle to run from each. Allows for refuelling each tank at separate locations to reduce the chances of getting contaminated fuel in both tanks, & doesn’t have to rely on some bit of computery techno wizardry to determine when it will work or won’t work, one less thing to go wrong in the middle of the outback. <Steps down off soapbox>.

[the evil twin]

Hiya Cuppa, pls excuse the snip...

But what is stupid, & makes no logical sense (to me) is the Patrol’s sub tank operation. Why on earth was it designed to pump from one tank to another ....

Because it is cheaper and less complex plumbing wise.
The Tojo system is a 'supply system' requires valving etc so that the two tanks are completely seperate incl fuel return.
The Patrol system is a 'transfer system' so is essentially just one BIG tank really.

Note that cheaper isn't necessarily better as one is mechanically complex and the other is electrically complex.
Dunno about the contaminated fuel scenario or not... I usually manage my fuel differently to that.

[bazzaboy]

But what is stupid, & makes no logical sense (to me) is the Patrol’s sub tank operation. Why on earth was it designed to pump from one tank to another & then pump it out of the main tank (which sits at the rear of the chassis - at least it does on my ute). Is there an advantage to this method I’m not seeing? If in every day use one uses only the main tank then the weight of fuel is in the worst position. Toyota’s have a separate pump from each tank & a switch to allow the vehicle to run from each. Allows for refuelling each tank at separate locations to reduce the chances of getting contaminated fuel in both tanks, & doesn’t have to rely on some bit of computery techno wizardry to determine when it will work or won’t work, one less thing to go wrong in the middle of the outback. <Steps down off soapbox>.

My two petrol 120 Prado were even easier. 185lts total in two tanks. As you feed from & empty the main tank, the second tank gravity feeds the main tank. Simple, and no small transfer pumps involved.