90 Series Prado Fuel Passage Sub Tank

[K & M McF Senior Member Find all posts View Profile Close K & M McF]

This has been covered many times before on Pradopoint. From my experience, if you use main and have full sub, nothing strange happens. If you use sub and have main full, main drops a little. If you alternate, it is hard to see any changes from one tank to another.

Also from experience, on a trip (in more remote areas especially) I would recommend using one tank till half, then the other till half, then the first one to a quarter and then the second to a quarter. Why? Because I once had the solenoid wires rip out meaning I had a sub tank that was full but could not access it and a main tank that was one quarter full. Luckily I was close to a town and also, as it turned out, I could have easily fixed the problem, but if it was a failed solenoid or a hole punctured in the full tank, I could have been in big problems.

[patrick_133 Lurker Find all posts View Profile Close patrick_133]

This has been covered many times before on Pradopoint. From my experience, if you use main and have full sub, nothing strange happens. If you use sub and have main full, main drops a little. If you alternate, it is hard to see any changes from one tank to another.

Also from experience, on a trip (in more remote areas especially) I would recommend using one tank till half, then the other till half, then the first one to a quarter and then the second to a quarter. Why? Because I once had the solenoid wires rip out meaning I had a sub tank that was full but could not access it and a main tank that was one quarter full. Luckily I was close to a town and also, as it turned out, I could have easily fixed the problem, but if it was a failed solenoid or a hole punctured in the full tank, I could have been in big problems.

Thank you,

I may end up looking for a auto technician to shut of this feature, It is easy enough to bypass the solenoid if you rip wires hoses etc, If you get a hole in a tank you should notice that tank start dropping (I have) and solve it, same as your fuel lines etc.

I have looked around on pradopoint but could not see this any where.

PS if you rip wires out all you have to do is swap the return and main lines around on the solenoid.

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

By what I'm reading I should not be loosing/Using any fuel from the main when I'm on the sub tank.

I think there must be something wrong with the ECU and drawing from both, I'm going to run the main dry (don't like doing this) and run on the sub and see what happens.

Then do the same in reverse, Run sub dry and run on main!

I do it all the time and have been doing so for the last 200 000km and makes no difference - why do you not like running the main tank dry ? my way of thinking if you continue running both tanks dry it will lower the chances of a build up of shit in the bottom of tanks.

[patrick_133 Lurker Find all posts View Profile Close patrick_133]

I do it all the time and have been doing so for the last 200 000km and makes no difference - why do you not like running the main tank dry ? my way of thinking if you continue running both tanks dry it will lower the chances of a build up of shit in the bottom of tanks.

I have not had this car from new so no idea what is in the bottom of the tank will have it cleaned first.

With electronic fuel injection, the impurities and dirt in the fuel tank gets sucked up into your fuel pump and pushed through your fuel filter. When the filter gets full or clogged and the fuel cant flow guess what...FUEL PUMP BURNS UP!

The fuel lines, if starved of fuel, might allow air to enter which is not correct. Its like running engine without engine oil. Fuel Lines are lubricated by fuel. If not done they are going to harm it.

I also need to find out if this Car draws from the bottom of the tank, if so I should not have an issue.

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

I am surprised at all the different theories on how the system works.
The owners manual states:
"Due to the fuel passage incorporated into the sub fuel tank system, the fuel in the sub tank increases as you consume fuel from the main fuel tank. This fuel passage is designed to encourage your use of the sub fuel tank from time to time so that the fuel pump within the sub fuel tank is properly lubricated"
Probably because a lot of the time the sub tank is not used regularly and this will help extend the life of the sub tank pump. The bled off is not controlled by the ECU but by the tank selector switch and the design of the valve which has a venturi action to bled off a portion of the main tank return.
Both the in tank pumps have "sock" prefilters fitted which should protect them from debris in the tanks, if the prefilters get blocked you will lose fuel pressure and have a loss in engine performance so you should not "cook" a pump as the pump will most likely still be immersed in (cooling) fuel.
My petrol Prado fuel system behaves in that manner and both diesel and petrol models use the same return valve assembly (diesel without in tank pumps), I have seen a fuel passage "disassembled" and it is just a small venturi so if your fuel system is adding fuel from sub to main then something is not right.

It really is a simple sysem but we seem to be making more complicated than it is.

Lee

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

I'd love to see a pic of this Venturi valve....
My 96 model petrol had 1 fuel return solenoid and 1 delivery tee valve....
I have converted it to diesel and had to take out the fuel pumps and put another solenoid in place of the delivery tee

[patrick_133 Lurker Find all posts View Profile Close patrick_133]

I am surprised at all the different theories on how the system works.
The owners manual states:
"Due to the fuel passage incorporated into the sub fuel tank system, the fuel in the sub tank increases as you consume fuel from the main fuel tank. This fuel passage is designed to encourage your use of the sub fuel tank from time to time so that the fuel pump within the sub fuel tank is properly lubricated"
Probably because a lot of the time the sub tank is not used regularly and this will help extend the life of the sub tank pump. The bled off is not controlled by the ECU but by the tank selector switch and the design of the valve which has a venturi action to bled off a portion of the main tank return.
Both the in tank pumps have "sock" prefilters fitted which should protect them from debris in the tanks, if the prefilters get blocked you will lose fuel pressure and have a loss in engine performance so you should not "cook" a pump as the pump will most likely still be immersed in (cooling) fuel.
My petrol Prado fuel system behaves in that manner and both diesel and petrol models use the same return valve assembly (diesel without in tank pumps), I have seen a fuel passage "disassembled" and it is just a small venturi so if your fuel system is adding fuel from sub to main then something is not right.

It really is a simple sysem but we seem to be making more complicated than it is.

Lee

As I said that makes 100% sense...

"Due to the fuel passage incorporated into the sub fuel tank system, the fuel in the sub tank increases as you consume fuel from the main fuel tank. This fuel passage is designed to encourage your use of the sub fuel tank from time to time so that the fuel pump within the sub fuel tank is properly lubricated"

But when im on SUB It is still using from main!

Done a 100km trip yesterday, main was FULL could not fit a drop more in to it, drove for 100KM on the SUB tank noticed BOTH gauges had dropped after 80KM at 100KM I refilled MAIN I was able to put 4LTRS in to main!

So for some Fuel states, when im on SUBTANK not touching MAIN at all, I am still using 4LTS Aprox from main!

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

Patrick,

Do you have a petrol or a diesel Prado?
If it is diesel and the soleniod fuel valve is not closing/sealing properly then it is possible the engine mounted fuel pump would draw from both tanks (probably depending on fuel levels).
If this is the case then if one tank is empty you could suck air into the system.
If it is petrol (with a "T" only) then without both in tank pumps running I don't see how it would draw on both.

I no longer have access to the cut up valve but I will see if I can source a picture or tech diagram of it.
Having to add a fuel supply solenoid for a diesel conversion is correct as the diesel "sucks" fuel from the tanks and a tee would allow fuel (or air) to be drawn from both tanks at once. Using the same Return valve system as the petrol results in a small quantity of diesel being diverted to the sub tank when using the main but as the quantity is small I believe it is not considered an issue.

Lee

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

This could be how the return valve operates but my conversion only uses and delivers fuel from what tank I've selected
The sub system was pretty complicated, I had to add a relay so the sub gauge light would work when selected ... Otherwise when on main it would indicate sub was in use...! 6000ks on it's still running perfect

[patrick_133 Lurker Find all posts View Profile Close patrick_133]

Well just a update thought I would run the sub dry, well that was my objective any way.

I have now driven 150 km with the needle bellow the empty, the main has dropped a considerable about, it appears that eave though sub is selected it I taking from main preventing it from running out

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

They must have different set ups for different models.

On my 2000 model diesel if I leave it switched to the SUB tank it will run dry and the engine stops while the main tank is full.

And the same happens the other way, run the main tank dry it stops even if the SUB is showing full.

This is factory standard as I have had this Prado TX since new, and it is still running great with its tanks working as I have mentioned above.

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

They must have different set ups for different models.

On my 2000 model diesel if I leave it switched to the SUB tank it will run dry and the engine stops while the main tank is full.

And the same happens the other way, run the main tank dry it stops even if the SUB is showing full.

This is factory standard as I have had this Prado TX since new, and it is still running great with its tanks working as I have mentioned above.

exactly how mine works

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

Patrick, is your Prado a petrol or diesel?

JKAF & Scott, my petrol Prado will do the same, if I run either tank out the engine stops. There is no automatic transfer or switching.
If Patrick's Prado is a V6 petrol, then both in tank pumps MUST be running all the time for it to do what it is if the sub tank is empty. My sub tank still has approx 18-20 litres in it when the gauge shows empty (50 litres to fill from E mark) I would be checking the wiring and relays very carefully as there is definitely something amiss with the wiring if that is the case. I can hear my pumps running but I have high volume pumps in my Prado, I would expect you could hear the standard pumps as well especially if the tank is empty or near empty.

Lee

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

They must have different set ups for different models.

On my 2000 model diesel if I leave it switched to the SUB tank it will run dry and the engine stops while the main tank is full.

And the same happens the other way, run the main tank dry it stops even if the SUB is showing full.

This is factory standard as I have had this Prado TX since new, and it is still running great with its tanks working as I have mentioned above.

Petrol models are set up the same. If I run the sub or main dry it will stop, but start up again when you switch to the other tank (if it has fuel), it will not be as big a problem as the diesel though...lol

[patrick_133 Lurker Find all posts View Profile Close patrick_133]

Patrick, is your Prado a petrol or diesel?

JKAF & Scott, my petrol Prado will do the same, if I run either tank out the engine stops. There is no automatic transfer or switching.
If Patrick's Prado is a V6 petrol, then both in tank pumps MUST be running all the time for it to do what it is if the sub tank is empty. My sub tank still has approx 18-20 litres in it when the gauge shows empty (50 litres to fill from E mark) I would be checking the wiring and relays very carefully as there is definitely something amiss with the wiring if that is the case. I can hear my pumps running but I have high volume pumps in my Prado, I would expect you could hear the standard pumps as well especially if the tank is empty or near empty.

Lee

Sorry guys thought I said its a Petrol 6 3.4ltr

Well 18-20 ltrs, I will keep driving then that's a lot after the empty line