"Priming" a Benz Unimog - How??





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  1. #1
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    Default "Priming" a Benz Unimog - How??

    Hi Guys

    I'm trying to start the red Doka 416, but it just stutters and then dies.

    We always "prime" it with that primer under the right front wheel, no problem then, but now that primer thingie stays "soft".

    I put 20 litre Diesel in it already - same issue.

    Do I need to "bleed"it or something??

    Car has stood still for a very long time, maybe a month, so I do suspect there can be some air in a pipe or something somewhere??

    Thanks, will post Pics if necessary.
    "Yes, I have a Bad Habit. I take Tea at Three".........Mick Jagger

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    Default Re: "Priming" a Benz Unimog - How??

    My W115 Covid project did the same. One of the fuel lines from the tank to the priming pump perished and had to be replaced.
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    Default Re: "Priming" a Benz Unimog - How??

    Quote Originally Posted by Tom13 View Post
    My W115 Covid project did the same. One of the fuel lines from the tank to the priming pump perished and had to be replaced.
    Thanks I thought it may also be something like that.........but this morning the pomp dingetjie did get hard, Mog idled 100%, then started huffing and puffing.

    I thought it could be fuel, and went and put in 20 litres.

    Now the pompie stays pap.

    So.........I'm thinking it was fuel, it ran out, and now it needs "bleeding??"??

    I'd like to drive the old girl around a bit, to home and back, just to get the parts moving a bit.
    "Yes, I have a Bad Habit. I take Tea at Three".........Mick Jagger

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    Default Re: "Priming" a Benz Unimog - How??

    Here's the pompie thingie with some small filter underneath.........the filter is about 3/4 full, is that correct??

    Then, that big bolt on my thumb - do you "bleed"it there??
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    "Yes, I have a Bad Habit. I take Tea at Three".........Mick Jagger

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    Default Re: "Priming" a Benz Unimog - How??

    Close up of the filter thingie. I see some gunk in there - how to clean that without causing some airlock or something??

    Thanks!!
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    Default Re: "Priming" a Benz Unimog - How??

    Sorry Guys, I just want to get this through.........if I hold that pompie thing in, the filter glass then empties with some tiny bubbles, if I release it it fills up the "glass" to full, and if I start pomping the diesel lever drops to around 3/4.................??
    "Yes, I have a Bad Habit. I take Tea at Three".........Mick Jagger

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    Default Re: "Priming" a Benz Unimog - How??

    I'm no expert but believe the dirt/gunk and the tiny air bubbles are not suppose to be there.
    Hopefully someone that knows the older diesel technology will be along soon.
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    Default Re: "Priming" a Benz Unimog - How??

    On my Merc the bleed pump pulls the diesel from the tank, through a small pre-filter and then pushes the diesel into the main diesel filter and then to the diesel pump. I disconnected the line where it enters the diesel pump and then kept priming until the diesel flowed from the tubing at the diesel pump.

    The pump on mine does not go hard since the excess diesel just gets returned to the diesel tank via a fuel line between the diesel pump and the diesel tank- there is no pressure build up at all.

    If the system is leak free, all the lines and filters should be filled with diesel all the time while the engine is running. If that sight glass below the pump runs dry there possibly could be a problem between the bleed pump and the diesel tank - air leak or a blocked filter in the tank if there is one.

    Maybe the Mog system works in a similar way.
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    Default Re: "Priming" a Benz Unimog - How??

    Thanks, got it sorted yesterday......just held that pompie thingie in a couple times, the diesel in the glass fills up each time and bubbles eventually disappeared.
    But I'll clean that glass, anyway.
    Not me, my son, I dont like fiddling with stuff like that.
    But ja, sorted, I'll probably fire up the old girl today and drive her around a bit, just to get fluids and parts moving a bit.

    As for that green Mog........well, that baby starts if you just look at her.
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    Default Re: "Priming" a Benz Unimog - How??

    Hi Petri

    A bit late on this thread, but for future reference:

    To clean the glass bowl on the primer pump - unscrew the little "wheel thingy" (highlighted in pic below) by hand. When it's loose, you can swivel it out of the way and drop the glass bowl straight down.
    Be careful - don't drop the glass bowl as they can break and then you have problems...

    Next time you need to bleed the fuel system - on top of each of the fuel filters there's a small screw. Loosen this screw and pump the hand pump until the bubbles stop coming out the top of the filters and you get clean fuel coming out. Tighten the two screws and she should start fairly easily.
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    Default Re: "Priming" a Benz Unimog - How??

    THANKS PAUL!!!

    That pompie - moet hy styf wees of nie noodwendig nie?? Die Mog start nou weer maklik, no issues, maar die pompie is nie so styf soos die groene sn nie??
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    Default Re: "Priming" a Benz Unimog - How??

    Quote Originally Posted by paulventer View Post
    Hi Petri

    A bit late on this thread, but for future reference:

    To clean the glass bowl on the primer pump - unscrew the little "wheel thingy" (highlighted in pic below) by hand. When it's loose, you can swivel it out of the way and drop the glass bowl straight down.
    Be careful - don't drop the glass bowl as they can break and then you have problems...

    Next time you need to bleed the fuel system - on top of each of the fuel filters there's a small screw. Loosen this screw and pump the hand pump until the bubbles stop coming out the top of the filters and you get clean fuel coming out. Tighten the two screws and she should start fairly easily.
    That's the way I remember it. Is there not a bleed point on the injector pump as well?
    Alan


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    Default Re: "Priming" a Benz Unimog - How??

    Quote Originally Posted by Petri Oosthuizen View Post
    THANKS PAUL!!!

    That pompie - moet hy styf wees of nie noodwendig nie?? Die Mog start nou weer maklik, no issues, maar die pompie is nie so styf soos die groene sn nie??
    Petri, no it doesn't become hard. When you pump it and the fuel is flowing, you will hear a zzzt zzzt from the back of the injector pump, well the side actually, between the injector pump and the engine block, there is a pipe coming out. It is a little ball bearing and a spring valve.
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    Default Re: "Priming" a Benz Unimog - How??

    Petri - one more tip:

    When you clean out the glass bowl thingy, make sure it seats properly on the rubber seal when you put it back. If it doesn't seat properly, you'll get an air leak which can cause the symptoms you've had.

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