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Baffling (head scratching)

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by Dean Fletcher, Nov 17, 2020.

  1. Dean Fletcher

    Dean Fletcher Senior Member

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    Your Mercedes:
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    So..... 4 weeks ago my wife said the car needs coolant as the sign came on. I topped it up a little and marked the bottle to see if it was a leak or actually just low... All good.
    5 days later I was on holiday got in it on Monday morning to go to Manchester top up coolant light again, so I topped it up and daringly took it on a 230 mile trip with 5L coolant in the boot. Got to Manchester and back no light, I thought great, Tuesday went to Carlisle probably about another 70 miles round trip no coolant light. Wednesday went to Bowness for wife's birthday probably 100 mile trip no coolant light.
    Used the car here and there over weekend all good.
    Wife used car to do shopping last Thursday still all good. Then................ She got in it today and......... Top up coolant light. So the car seems fine when it's being ran out daily but when it sat for a while seems to leak. Any ideas?
    I checked the coolant daily when I was off work and didn't seem to go down.
     
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  2. EmilysDad

    EmilysDad Senior Member

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    iffy header tank cap?
     
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  3. Uncle Benz

    Uncle Benz Senior Member

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    Petrol or diesel? Plastic coolant parts like to do this. They drip when cold, but when warm they expand and seal themselves up.
     
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  4. Kev555

    Kev555 Senior Member

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    Strange alright, If you've got a garage put it in with cardboard underneath to see if its an external leak hopefully if its losing enough to mark the cardboard
     
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  5. Kev555

    Kev555 Senior Member

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    Think you could be on the money there Uncle Benz:D
     
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  6. OP
    Dean Fletcher

    Dean Fletcher Senior Member

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    Diesel, that's make sense now
     
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  7. Uncle Benz

    Uncle Benz Senior Member

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    Om651 then. Plastic water pump, plastic thermostat and the plastic piece that holds the fuel filter. All of them are known trouble spots for coolant leaks. Shine a torch down around the fuel filter sides. You can usually see water laying there or the white crust where it has dried
     
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  8. OP
    Dean Fletcher

    Dean Fletcher Senior Member

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    Thanks ill have a look.
     
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  9. Jim2

    Jim2 Senior Member

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    Had the very same problem with my 2014 E class with the OM651 engine, some times it only lasted days between needing a top-up, sometimes a week or two. No visible signs of any leaking. As it was still under warranty, I took it back to the dealership who solved it in a matter of hours by replacing the fuel filter housing, its a well known fault in them and they keep a stock of these filter housings in stock.
     
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  10. OP
    Dean Fletcher

    Dean Fletcher Senior Member

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    Cheers Jim ill look into that. Just waiting for a nice day to get me torch out. :D
     
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  11. EmilysDad

    EmilysDad Senior Member

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    I'm confused!?!? How does a faulty fuel filter housing affect the coolant loss?
     
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  12. Uncle Benz

    Uncle Benz Senior Member

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    The fuel filter just sits in a receptacle that is part of a larger plastic part. It also is a coolant pipe. It's one big bit.
     
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  13. EmilysDad

    EmilysDad Senior Member

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    Ah! Thanks :)
     
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  14. Kev555

    Kev555 Senior Member

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    Them crap injectors must like their diesel warm:D
     
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  15. mattkh

    mattkh Senior Member

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    Warm diesel in a harsh winter is a god send.
     
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  16. Jim2

    Jim2 Senior Member

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    As Uncle Benz says its a "T*T The housing is bolted to the block, and is connected to the engine cooling system so when the thermostat opens the circulation, the hot water circulates around the fuel filter in the bowl warming the fuel.Problem is in early models, it was held in place with only two bolts, which allowed the seal to leak. The replacement ones use 3 bolts and are a better job........so far !!!:geek:
     
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  17. ajlsl600

    ajlsl600 Senior Member

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    As usual r and d on customer cheap version on production line, proper job at pts counter along with card reader. Same with water pump.
     
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  18. OP
    Dean Fletcher

    Dean Fletcher Senior Member

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    So after having a quick look just now I see liquid which I suspect to be coolant just beside the fuel filter. What do you think. IMG_20201119_181745.jpg IMG_20201119_180759.jpg
     
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  19. Jim2

    Jim2 Senior Member

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    When mine leaked, it showed very little outward signs of leakage, and to be honest, I'm not sure if that is coolant residue or not. Problem is that the leaking is done when the vehicle is moving, and that tends to dissipate the coolant. But if it were anywhere else, and leaking at the rate yours is, should be very obvious where its leaking from....internally, wet / damp carpets, radiator, water pump, header tank cap, will definitely show signs of leaking. Mine has not lost any water since the filter housing was replaced. And the garage knew exactly what it was the minute it was described to them...and like I said earlier... they always keep some in stock. Its not that big ( or expensive ) a job, and once its done, you can forget about it. But the only real way to be sure is to remove it and check the gasket / seal.
     
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  20. Jim2

    Jim2 Senior Member

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    When mine leaked, it showed very little outward signs of leaking, and I am not sure from your pics if those stains are coolant or not. Chances are that they are though. Only way to confirm it will be to remove it and check the seal.When you have a leak like yours, should be obvious..damp carpets, strains around the water pump,header tank cap, radiator etc. If those are not present, it's the filter housing, and as the car will be moving, the water will be dispersed.
     

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