Question about W124 Estate/ Wagon fuel tank connections

Discussion in 'Engine' started by chilsta, Oct 20, 2010.

  1. chilsta

    chilsta Active Member

    Messages:
    103
    Joined:
    Jul 18, 2010
    Car:
    '94 S124 E300D
    I'm upgrading the fuel system on my 300TD, which I'm going to write about on my diary thread soon, but in the meantime I have a question.

    A replacement tank was fitted a few years ago, before I bought the car.

    The metal fuel lines running the length of the car are both 8mm OD, but the tank has one 8mm & one 10mm, the upper connection being the 10mm.
    (Someone had used a 10mm rubber hose on the 10mm connection from the tank and just clamped it down onto the 8mm undercar pipe.)

    Logic would suggest that the larger bore would be for the send pipe, but the return hose was connected to it.

    (My guess is that the original tank had both 8mm send/returns, but this is a tank from a multivalve or turbo with higher fuel flow needed and thus the larger send capacity.)

    Does anyone know whether my thoughts about the larger bore being the send are correct and the tank had been plumbed up wrong, and/or have a diagram of the connections to the fuel tank?

    Thanks.
     
  2. bolide

    bolide MB Enthusiast

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  3. OP
    OP
    chilsta

    chilsta Active Member

    Messages:
    103
    Joined:
    Jul 18, 2010
    Car:
    '94 S124 E300D
    Hi Nick, thanks for your reply.

    I haven't been able to get into the Russian EPC since I bought my car. Seems the only way is to register, but the registration page is in Russian and I got stuck there.

    The larger 10mm pipe is above the 8mm one.

    I've since found this diagram online:

    [​IMG]


    which shows the send (69) and return (70), but annoyingly it's showing the larger pipe below the small one, whereas mine's the other way round.
    Mine doesn't have the leak line (72) either (maybe that's a petrol thing).

    Maybe the internals of the tanks were changed at some point and the replacement that's in my car is from a later model than when this manual was made..?

    The car ran fine connected up the way that it was, which is the same as the diagram. It's just the reversed large & small pipes that don't add up.

    I think I'll connect it back up as it was and hope for the best, unless some further light is shed.
     
  4. spock500

    spock500 Active Member

    Messages:
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    Apr 1, 2008
    Location:
    Milton Keynes
    Car:
    S124
    I have seen a few posts from owners who have expeienced a blocked strainer causing restricted flow/non starting, to overcome this (and being lazy:rolleyes: ) they switch the feed line for the return bypassing the strainer altogether -


    Maybe this has happened on yours at some stage?
     
    1 person likes this.
  5. OP
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    chilsta

    chilsta Active Member

    Messages:
    103
    Joined:
    Jul 18, 2010
    Car:
    '94 S124 E300D
    Hmmm, that's interesting.

    Part of the reason of this work is that I've been experiencing fuel delivery issues. I've actually now removed the fuel strainer and added a glass bowl filter which is mounted to the inner wing.

    I recently ran my (and probably the car's) first half tank of veggie oil and presumed that my problems were a result of sludge in the tank being dissolved by the veggie oil, however the strainer was completely clean. I was wondering how the strainer would be affected if the send/return had been set up round the wrong way. Thanks for confirming my suspicions, and letting me know that the car will run OK if they're on round the wrong way, which is my main concern with a 300 mile round trip in the next couple of days.

    The tank was replaced with a recon from Dronsfields 4.5 years/ 10k miles ago, and I couldn't see any sign of sludge through the strainer hole. If they were on round the wrong way I suspect it was in error.

    When dismantling the old fuel lines I found that nearly all of the connections were loose and there was visible weeping at the tank send/return joins. Seems likely that the higher viscosity of the veggie oil has caused the lift pump to pull in air through already weak joints throughout the system.
    The new larger bore nylon fuel lines and spring clips around the rubber joins should ensure that there won't be any more of that going on :)
     
    Last edited: Oct 20, 2010
  6. spock500

    spock500 Active Member

    Messages:
    727
    Joined:
    Apr 1, 2008
    Location:
    Milton Keynes
    Car:
    S124
    The lines being around the wrong way will possibly have an effect on the suction required to draw the fuel as each pipe has a different internal arrangement.

    The feed pipe for example sits usually inside a chamber to avoid losing fuel on corners - the return on the other hand goes through an internal pipe before depositing the hot fuel back near the above chamber, drawing fuel from this would be a strain long term.

    This is the tank from a 300TD courtesy anddy but it gives you an idea;

    [​IMG]

    [​IMG]
     
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