Diff oil and petrol tank operation

[Pepsi Junior Member Find all posts View Profile Close Pepsi]

Hi All

Pick my Prado up this Saturday and have a couple of questions I cant find the answer to.
Firstly the front and rear diff oils from penrite are the same 80w-90 but the rear is recommended to add 150ml of limslip oil additive.
Can someone tell me what this does and if I do not add it what are the ramifications.

Also the dual petrol tank operation, I understand how the the guage works but how do the two tanks work together, are they joined by a pump, are the gravity fed and also how do you fill them, do you need to switch tanks to fill both.

Thanks
pepsi

[Bushbasher Out of control poster! Find all posts View Profile Close Bushbasher]

No switching on the tanks. Fuel is transferred from rear tank to the front tank and then through to the engine and return automatically. There is no manual ability to switch tanks like on the old 90 series. The rear diff is an LSD so needs an appropriate oil.

[Pepsi Junior Member Find all posts View Profile Close Pepsi]

Thanks bushbasher
I read where the gauge changes to the first tank when the second tank gets down to approximately 15l of fuel left.
Does this system actually use the full amount of fuel as I would hate to run out and still find 15l left in the tank that I cant use.
Cheers
Rob

[AJ120 Out of control poster! Find all posts View Profile Close AJ120]

Thanks bushbasher
I read where the gauge changes to the first tank when the second tank gets down to approximately 15l of fuel left.
Does this system actually use the full amount of fuel as I would hate to run out and still find 15l left in the tank that I cant use.
Cheers
Rob

That's not correct, you use the fuel in the rear tank first, that tank holds 93 litres, the gauge will drop from full to just under half as this tank is used. Once that tank is empty the gauge jumps to full and you have 87 litres in the front tank. The gauge will drop down and just before empty the fuel light will come on indicating 15 lts left.

If you run out of fuel, your out of fuel, you are probably thinking of the 150 series which I think is a bit different.

Cheers Andrew

[topic97 Senior Member Find all posts View Profile Close topic97]

Well.... I just conducted a test with mine as im having fuel gauge issues it seems.
I just finished running it dry from two full tanks & found that I ended up doing an extra 180ks after the on board computer said I had 0ks to empty.
The fuel warning light had been on a fair while before that point too - hence why i could only get about 130-140 litres into it when the fuel light comes on.
So realistically I did at least 250ks extra town driving after the fuel light came on!

On a side note, I drive a petrol so wouldn't suggest doing this test in a diesel...

[topic97 Senior Member Find all posts View Profile Close topic97]

Thanks bushbasher
I read where the gauge changes to the first tank when the second tank gets down to approximately 15l of fuel left.
Does this system actually use the full amount of fuel as I would hate to run out and still find 15l left in the tank that I cant use.
Cheers
Rob

And after monitoring my fuel usage I wouldn't be surprised if this is true.
For some reason my first tank seems to go a lot quicker than the second tank - and im talking k's wise, not gauge wise, and then it seems to stick around the full mark on the last 90l for a long time.

My theory is that it changes to the main tank with some left in the rear tank, but that amount still drains into the front tank until empty.

Thats my theory anyway. lol

[AJ120 Out of control poster! Find all posts View Profile Close AJ120]

Both mine have been the other way round, the first tank gets me a lot further than the second tank.

Cheers Andrew

[r4ndll Avid PP Poster! Find all posts View Profile Close r4ndll]

Direct from a workshop manual:
"The sub fuel tank has no fuel pump. Instead fuel is drawn into the main tank via a jet pump which is a small valve in the main tank. An electric fuel pump within the main tank pumps fuel from the main tank through a fuel filter mounted near the tank and back into the main tank through a Venturi in the jet pump. This Venturi creates a low pressure beneath itself where there is an orifce connected to a fuel line that is in turn connected to the sub fuel tank. The low pressure draws fuel from the sub tank into the main fuel tank.
This operation is constant while the engine is running and once the fuel level in the main tank reaches a pre determined amount, the weight of the fuel in the main tank will slow down the amount of fuel being drawn from the sub fuel tank to the main fuel tank...

...when being filled, a t-piece in the filler neck will direct approximately 80% of the the fuel to the main tank and about 20% to the sub fuel tank"

[topic97 Senior Member Find all posts View Profile Close topic97]

Both mine have been the other way round, the first tank gets me a lot further than the second tank.

Cheers Andrew

Yeah its odd, you read so much mixed stuff on how it works.
Its like they all have a mind of their own! haha

[Pepsi Junior Member Find all posts View Profile Close Pepsi]

Now i am really confused, but as i have not got my car yet i will try it and see if i can make sense of it.
No doubt i will have a completely different experience. Haha
Thanks for all the replies

[Ozpat Advanced Member Find all posts View Profile Close Ozpat]

Direct from a workshop manual:
"...when being filled, a t-piece in the filler neck will direct approximately 80% of the fuel to the main tank and about 20% to the sub fuel tank"

So in the 120 which is the main tank and which is the sub?

[Bushbasher Out of control poster! Find all posts View Profile Close Bushbasher]

Sometimes my 90L light activates and scanguage says I have only got 60 odd litres left. I once drove 135km on "empty" with the orange light on only to fuel up and find there was over 11 L left. It's neither a consistent nor an accurate set-up that's for sure.

[Guest Close Guest]

Now i am really confused, but as i have not got my car yet i will try it and see if i can make sense of it.
No doubt i will have a completely different experience. Haha
Thanks for all the replies

What you do is fill it up till full. Then drive until the fuel light comes on and fill it up to full again. Now calculate the fuel economy and from there you'll know your range. Now ignore the fuel gauge and work off your calculated range. This would only work if you are going to be driving in the same manner. Then once you go on a road trip, your range will change, and same if you are going offroad, the range will change again. But at least you have some ballpark figure to reference.

[topic97 Senior Member Find all posts View Profile Close topic97]

What you do is fill it up till full. Then drive until the fuel light comes on and fill it up to full again. Now calculate the fuel economy and from there you'll know your range. Now ignore the fuel gauge and work off your calculated range. This would only work if you are going to be driving in the same manner. Then once you go on a road trip, your range will change, and same if you are going offroad, the range will change again. But at least you have some ballpark figure to reference.

Yep, exactly what Im doing now. Around town ill drive it till the light comes on then refill - but at least i know now how far I can really get when the fuel light comes on.

[topic97 Senior Member Find all posts View Profile Close topic97]

So in the 120 which is the main tank and which is the sub?

The tank on the left hand side is the main one, the rear tank is the sub.
Well sorta sub - they kinda work in tandem the way they are set up.