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  1. #1

    Fuel Management Dual Tanks

    I have 2014 Prado 150 series D4D. I am trying to get an understanding of how fuel is managed to, from and between the fitted dual fuel tanks, main and secondary. I'm aware that fuel is transferred (pumped) from main to engine and return (for cooling purposes) at 60.0L/hour. How fuel is distributed and sequenced between tanks is the mystery for me. My questions therefore are (1) When refueling, does main fill first then overflow to secondary, or do they fill simultaneously and equally? (2) During consumption, in what sequence do the tanks drain e.g. (a) simultaneously and equally (b) main first followed by transfer, secondary to main (c) main, to a certain residual volume then transfer, secondary to main (d) other? Also, how is fuel transferred between secondary and main, pumped, siphoned or drained? And further, what is the role of the so called "transfer pump", inter-tank fuel transfer or transfer between tank and engine, or both? When considering the possibility of water contamination, these would seem important questions to understand? Cheers.

  2. #2
    Member
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    the transfer "Pump" between the two tanks is just a venturi effect.

    the return fuel goes into a nozzle in the main tank which draws fuel across from the secondary tank.

    There is only 1 fuel pump in the main tank.

    So your engine is always drawing fuel from the main tank. but its constantly being topped up by the 2nd tank as the engine runs.

    when you fill up its dropping the fuel into the 2nd tank and it flows across to the primary.
    so say both tank are empty. you put 50L in, it will evenly fill both tanks, as soon as the engine starts it transfers everything it can into the primary tank and keeps transferring fuel as quickly as it's used.

    Good Points of the Venturi System;
    Never have stale fuel in tank
    no 2nd pump to fail, very simple system.

    Bad Points
    If you get contaminated fuel its mixed very quickly across both tanks.
    if you get a puncture in your main tank there is no isolating it and unless resolved you will drain all the fuel from both tanks.

    Last edited by HugoStiglitz; 11-01-2017 at 08:26 AM.

  3. #3
    Junior Member
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    Quote Originally Posted by HugoStiglitz View Post

    when you fill up its dropping the fuel into the 2nd tank and it flows across to the primary.
    so say both tank are empty. you put 50L in, it will evenly fill both tanks, as soon as the engine starts it transfers everything it can into the primary tank and keeps transferring fuel as quickly as it's used.
    I believe it's a common issue getting completely full tanks at the bowser, would you be able to get the job done quicker and more successfully if the engine is running?

  4. #4
    Deleted
    Last edited by Poppy Joe; 13-01-2017 at 06:01 PM.
    150 GXL Diesel Auto March 2010 TJM Suspension, General Grabber 265/70 AT2s. Snorkel, Dual batteries.

  5. #5
    Junior Member
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    Jan 2010
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    Pt Lincoln, SA
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    70
    Quote Originally Posted by Poppy Joe View Post
    What is the job of the pump in the main tank.
    Regards Joe
    The pump in the main tank is to get the fuel to the engine.....

  6. #6
    Deleted
    Last edited by Poppy Joe; 13-01-2017 at 06:00 PM.
    150 GXL Diesel Auto March 2010 TJM Suspension, General Grabber 265/70 AT2s. Snorkel, Dual batteries.

  7. #7
    Many thanks for your advice Hugo. Sorry re my tardy reply. I did read your post on the day, just before heading off for a vehicle inspection under warranty. My suspicion is that I have incurred water contamination during a 150L fill. Current evidence is, from a fuel sample taken a some point tank side of the filter, no water evident, but sparse deposits of what appeared to me to be fine metal fragments. I'm assuming contamination has not passed the filter. Faulty injectors have been replaced (car has only travelled 29,000 kms) and I suspect another injector is faulty (knock) but diagnostics suggest compliance (Toyota dealer's assessment). It still could be that residual water (if that form of contamination has occurred) is somewhere in the fuel management system - in my view.
    As a general observation, looking at the diagram accompanying your notes, that vacuum intake point could be problematic for contamination, depending on where it is placed and what filtering of air, if any, takes place. I also wonder about water condensation in those tanks as fuel depletes and is replaced by air? The observation game goes on. Thanks again for your input Hugo. Gerundivus.

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