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Thread: Something doesnt sound logical here

  1. 8th February 2015, 10:14 PM #1
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    sierrafery
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    Something doesnt sound logical here

    Guys, i'm thinking and overthinking on this and doesnt seem right to me, starting from here:
    Quote Originally Posted by COOLING SYSTEM - TD5; DESCRIPTION AND OPERATION 26-1-7
    Fuel cooler
    The fuel cooler is located on the right hand side of the engine and is attached to the inlet manifold. The cooler is
    cylindrical in design and has a coolant feed connection at its forward end. A 'T' connection at the rear of the cooler
    provides a connection for the coolant return from the heater matrix and coolant return from the fuel cooler.
    The 'T' connection houses a thermostat which opens at approximately 82C. This prevents the cooler operating in
    cold climates.
    Two quick release couplings on the cooler allow for the connection of the fuel feed from the pressure regulator and
    return to the fuel tank. A counter flow system is used within the cooler.
    Fuel flows around a coolant jacket within the cooler and flows from the back to the front of the cooler. As the hot fuel
    cools travelling slowly forwards it meets progressively colder coolant     travelling in the opposite direction maintaining a
    differential cooling effect.
    correct me if i'm wrong but the fuel goes into the cooler on the return as it comes out from the FPR where the temp sensor is, all the official diagnostic guides are stating that in normal operating conditions the fuel temp is 10*C below the coolant temp, confirmed by loads of live data logs i've seen in which actually 75*C fuel temp was tops... so what's the purpose of that cooler then???...other than being friggin' expensive and commonly be the source of coolant leaks or even worst fuel in coolant ingress issues???, unless there's some reason to heat up the fuel to the coolant's temp which i'm missing but then they should have named it ''fuel heater'' not ''cooler''... IMO this bit is completely useless there so as mine started to leak i'm thinking seriously to bypass and get rid of it completely

    somebody tell me what i'm missing here
    Discovery Td5 (2000), manual, tuned
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  2. 8th February 2015, 10:59 PM #2
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    Blknight.aus
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    wait till your working the engine up on a 40 degree day hitting something like towoomba rnge with a 3t trailer on the tail and a full load of tools in the back.

    the fuel temps come right up trying to keep the injectors cool and the fuel gallery then becomes a part of the coolant system for the head itself.

    contra flow through the cooler simply means the hot fuel enters the opposite side to the cool coolant inlet side.

    at peak load and combustion pressures the flame front temperatures are so high that without the extra cooling of the injectors by the fuel system the temperature in the injector nozzles is above the cracking temp of diesel. If the tank was low on fuel it wouldnt take all that long for the fuel system temps to get up to the point wehere it would be bad for the pump, tank plastics

    so yes, under most circumstances you dont really "need" the fuel cooler, but when you do need it its a good thing to have.
    Dave

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  3. 8th February 2015, 11:10 PM #3
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    Thanks for the explanation, my problem is that in all the live data logs i've seen from other's and i have nanocom on board as instrument on mine all the time i've never seen higher fuel temp than coolant temp readings even though i'm towing only a 2.5t boat, so as the fuel temp sensor is before the cooler in the FPR on the return line(so after the injectors?) it means that after the cooler if both temps are getting close that ''cooler'' is actually a heater ... i didn get rid of it yet as i have serious doubts that's why i'm asking
    Discovery Td5 (2000), manual, tuned
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  4. 9th February 2015, 12:02 AM #4
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    from memory and its been a while since Ive had to look at it the fuel temp sensor is before the head, and is reading the temperature of the fuel going into the engine.

    the fuel temp sensor is there to tell the ECU what temp the fuel is in the head so it can compensate the injection quantity for the loss of fuel density s the temp goes up.
    Dave

    "In a Landrover the other vehicle is your crumple zone."

    For spelling call Rogets, for mechanicing call me.

    Fozzy, 2.25D SIII Ex DCA Ute
    Tdi autoManual d1 (gave it to the Mupion)
    Archaeoptersix 1990 6x6 dual cab(This things staying)


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  5. 9th February 2015, 12:32 AM #5
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    Yes, here starts the real dillema cos both the fuel feed and return are connected to the regulator and the temp sensor is screwed in it, i dont know how it's internal flow is but the main amount of the fuel return is part of the feed which is blocked by the regulator to not exceed 4 bar as the pump's delivery is higher and the other part of the return is the fuel which wasn't atomised and both coming out through the same port,
    ...The regulator maintains the fuel pump delivery pressure at 4 bar (58 lbf.in 2 ). When the fuel pressure exceeds 4 bar
    (58 lbf.in 2 ), the regulator opens and allows fuel to return to the fuel tank via the fuel cooler....
    as i understood the higly pressurised fuel which gets hot due to injection is also "consumed" in the combustion so that will not come back into the return anyway ... so only the internal flow diagram of the FPR would enlight me on this to see if or how the return from the head can or can not affect the FT sensor reading but i couldn't find such thing, see attachments(neglect the red parts , it was for other thing) maybe you understand better, thank you for all your interventions so far, i really want to figure this out and im even up to insert a gauge instead of the cooler to see what happens
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    Discovery Td5 (2000), manual, tuned
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  6. 9th February 2015, 07:11 AM #6
    Graeme
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    My '02 TD5 D2's fuel temperature reading was ignored by the ecm, as noted on reports of functions/options enabled in its ecm.

    The fuel cooler is to cool the fuel returning to the tank because it gets priority for fuel being returned to the engine from the pump.
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  7. 9th February 2015, 07:30 AM #7
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    Yes but as things are looking it seems that the cooler doesnt cool the fuel but heats it
    Discovery Td5 (2000), manual, tuned
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  8. 9th February 2015, 12:22 PM #8
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    Coolant from the heater matrix then passes thru the fuel cooler tee branches it cannot flow into the cooler.

    The cooler thermostat sensing bulb is located upstream of the cooler t'stat valve.

    When coolant inside the cooler reaches the 82c the t'stat valve opens allowing coolant from rad (front) to flow thru to the cooler tee.
    (the bottom tee outlet is piped thru to coolant pump suction)

    Mine upon testing wouldn't open till 96c so I removed the thermostat and threw in a bin
    Been running without since just like the MY04 D2a's


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  9. 9th February 2015, 01:32 PM #9
    PhilipA
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    It's like transmission oil coolers in radiators.

    They heat until the desired temperature is reached eg whatever the temp is in the RH radiator tank in an RRC, then they cool.

    Regards Philip A
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  10. 9th February 2015, 08:17 PM #10
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    just from those diagrams.

    fuel go into the regulator block
    then it hits the pressure regulator
    from there it diverts to the head via the temp sensor and the excess runs to the cooler
    the return from the block comes from the front and joins the flow back to the cooler.

    effctively while the fuel from the tank is cooler than 82 degrees the coolers not doing much for you, when the fuel in the tank gets hot thats when the cooler comes into full effect.
    Dave

    "In a Landrover the other vehicle is your crumple zone."

    For spelling call Rogets, for mechanicing call me.

    Fozzy, 2.25D SIII Ex DCA Ute
    Tdi autoManual d1 (gave it to the Mupion)
    Archaeoptersix 1990 6x6 dual cab(This things staying)


    If you've benefited from one or more of my posts please remember, your taxes paid for my skill sets, I'm just trying to make sure you get your monies worth.
    If you think you're in front on the deal, pay it forwards.
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