Prado 120 Series tanks

I recall someone on this site stating that the fuel moves from the auxilliary tank to the main tank via a venturi system so that the fuel in the 2nd tank is topping up the 1st tank all the time.

I am not 100% on this, but do some searches.

yep, that's how I've read it works, so you're really using the 2nd tank 1st!

The gauge takes a little bit of getting used to, once it gets to helf way* it flicks back to full again and the "90L to go" light comes on (and acts like a normal fuel gauge)

* half way means about 100L, not 90 in my experience.

So what you are both saying is that there is no chance of fuel sitting in the tank going bad because the 2nd tank drains into the first tank.

That would mean that when you fill up after the 90L to go light comes on that you are topping up both tanks.

Do I have that correct.

Thank you for the answers.

That has taken a bit of a weight off my shoulders.

I envisaged having to use 170 litres to use the fuel up and then having to find $230 to fill it all again.

Good stuff

Thats totally different to the 90 series. With the 90 series even when running on main tank when you first turn ignition on the green light on the reserve tank lights up, once started it flicks back over to main BUT every now and then it transfers from the main to the reserve tank whilst running off main tank. I did notice this last week that when I first got the vehicle the reserve was on half and I was running off it. I whacked $50 in the main and switched over to main but by the end of the week the reserve was nearly full. Read the service books and this is normal for this procedure to happen. Also spoke to a bloke at work and he said yep all normal. But my mate has the 120 series and said is a pain in the ar#e trying to work out his fuel consumption just running off the first tank of fuel but mine is the same with the way it works. Only way I reckon is fill both up chockers drive around then refill both again. Regards Steve M

That was possibly me Juzzie. The 120 uses an ejector pump (no moving parts) which is located in the main tank to continuously transfer fuel from the sub tank to the main. Because it is a low pressure transfer system it just stops whenever the main is full. The fuel for the engine is drawn from the main tank at all times. So, if the main tank's full and if there is fuel in the sub tank it just transfers at the engine consumption rate.

Therefore there's no chance you will end up with "stale" fuel in your system.

The downside of this type of system is that if you hole either tank you run the risk of losing most, if not all of your fuel.

Holing the main is the most serious scenario, because it will empty out (whilst still transferring fuel from the sub). Then there's no way to transfer fuel from the sub (until at least you can get the leak fixed and engine started, which will run the ejector pump and transfer fuel :-) The problem here is that while all this is happening a lot of fuel from your sub will be transferred into the main (which is draining through the leak). So you're losing some of its contents even though it's not leaking :-(

If you hole the sub, then you just lose its contents.

With a selectable tank system ala 90 series you are afforded some protection from the first problem.

We have several of these pumps in our planes. They run automatically and never break down. Quite ingenious actually :-)