2000 E46 318i - Coolant leak onto top of expansion tank

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  1. 2000 E46 318i - Coolant leak onto top of expansion tank 
    #1
    Bimmer Fan
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    BMW318TOURING's Car Details
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    318i SE
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    1999
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    I've been having to top up my coolant every now and again, approx 0.5L per 500 miles, but couldn't see any evidence of a leak until today after I'd returned from a decent motorway run. (I was suspecting a possible HG issue, so am quite relieved!)

    I have a small amount of coolant sitting on the ridge around the top of the expansion tank. This then drips down onto the undertray where it evaporates. There is no evidence that coolant is being sprayed around under pressure, it just seems to collect and drip.

    6O9swYq7.jpg

    You can see the coolant collecting in the above picture.

    I've read about problems with the expansion tank hairline cracks, but I can't see any obvious cracks and as the coolant is collecting at the top of the tank well above where the usual hairline cracks appear. I can't see anything obvious from the other suspect - the top coolant hose.

    Any pointers?

    I know the general advice is to replace as much as possible, but the car is a cheap runabout so I don't want to throw money at it in an effort to get rid of the problem through trial-and-error.

    BMW have quoted me 33 for the top hose and 74 for the expansion tank; does this seem reasonable? Any pointers to good online retailers for BMW OEM parts?
     
     

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    #2
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    Dez-Derek's Car Details
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    I can't see clearly from your picture. Is there any coolant coming from the cap?

    My cooling system seemed to get too pressurised....turns out it was the HG...my suspicion was backed up by bubbles in the expansion bottle when the engine was running. But your's doesn't seem that serious for now.

    I replaced my expansion bottle and rear part of my exhaust for 150 (including labour) at Halfords Autocentre garage and so far they have been good.

    Driven by experience and pleasure
     
     

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    I've done a bit more digging: The leak is coming from the join between the top hose and the expansion tank.

    I've taken it all apart and cleaned it up before putting it back together. If anything it's now leaking more!

    Trouble is, I cannot identify if the it's the top hose or expansion tank that is causing the problem. The connection between the two doesn't seem very good either...
     
     

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    #4
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    Right, took the top hose apart and removed and refitted the o-rings. Refilled the system and bled the coolant.

    No leaks from that area now!

    BUT, after a drive to get the car nice and hot, the coolant comes out of the expansion tank cap when the engine has been switched off

    I'm sure I bled the system properly, there was the right amount of coolant in it.

    Is this a symptom of over pressurization? What causes this?
     
     

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    #5
    kib
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    it could be it is not bled enough they can be a pain to get right.some people fill it up from
    top hose till water comes out but do it very slow,there is a write up somewere have a look.
     
     

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    #6
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    Quote Originally Posted by BMW318TOURING View Post
    Is this a symptom of over pressurization? What causes this?
    Remove the radiator cap, start car and let it run for a few minutes......see if you notice any bubbles.

    Driven by experience and pleasure
     
     

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