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Thread: Draining 2GM 20

  1. #1
    Join Date
    Nov 2016
    Posts
    142

    Default Draining 2GM 20

    Went to try and service my 2GM 20 for the first time and wanted to drain the raw water coolant so I could check the impeller. The drain seems to consist of two threaded nuts attached to the cylinder head with a bolt running through the centre. I undid the bolt and no water came out. I wiggled a screwdriver in it to see if it was blocked, but appeared clear.

    Do you have to undo the whole assembly or am I missing something? Alternatively is there another way to drain the raw water.

    Thanks for any assistance

    Andy

  2. #2
    Join Date
    May 2001
    Location
    North Wales, sailing Aegean Sea or Menai Strait
    Posts
    21,453

    Default Re: Draining 2GM 20

    Just take the cover off the pump, or probably remove a hose as you will usually need to do this to turn the pump round.
    Answers to some technical queries at new website http://coxeng.co.uk

  3. #3
    Join Date
    Nov 2009
    Location
    Home UK Midlands / Boat Croatia
    Posts
    18,295

    Default Re: Draining 2GM 20

    Quote Originally Posted by Andibs View Post
    Went to try and service my 2GM 20 for the first time and wanted to drain the raw water coolant so I could check the impeller. The drain seems to consist of two threaded nuts attached to the cylinder head with a bolt running through the centre. I undid the bolt and no water came out. I wiggled a screwdriver in it to see if it was blocked, but appeared clear.

    Do you have to undo the whole assembly or am I missing something? Alternatively is there another way to drain the raw water.

    Thanks for any assistance

    Andy
    I don't understand why a raw water drain would be anywhere near the cylinder head? Surely that's too high to be a drain? It could be a vent to let air in but, as Vyv says, just remove a hose or the pump cover and you won't need to let air in.

    Richard

  4. #4
    Join Date
    Jul 2001
    Location
    Cyberspace
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    34,481

    Default Re: Draining 2GM 20

    It's seawater... Just take the pump cover off and let it drain into the bilge.

    - W

  5. #5
    Join Date
    May 2017
    Posts
    96

    Default Re: Draining 2GM 20

    2gm20 seawater drain is a black knurled plastic knob on stbd side of block below exhaust manifold. It unscrews from a bronze coloured casting which has a clear tube extending towards bilge. However it easily sludges up and if you unscrew it completely and remove it you can them usually get it to drain by poking wire in.
    But quickest is to take tube off water pump which you have itself to take off to change impeller.....

  6. #6
    Join Date
    Jan 2003
    Location
    Clyde
    Posts
    7,242

    Default Re: Draining 2GM 20

    Quote Originally Posted by blan321 View Post
    2gm20 seawater drain is a black knurled plastic knob on stbd side of block below exhaust manifold. It unscrews from a bronze coloured casting which has a clear tube extending towards bilge. However it easily sludges up and if you unscrew it completely and remove it you can them usually get it to drain by poking wire in.
    But quickest is to take tube off water pump which you have itself to take off to change impeller.....
    Spot on. That drain plug gets bunged up too. A stiff wire will clear it out

  7. #7
    Join Date
    Mar 2004
    Posts
    5,858

    Default Re: Draining 2GM 20

    rinse all of the external bits with fresh water to get rid of the salt / rust risk.

  8. #8
    Join Date
    Apr 2005
    Location
    Shropshire
    Posts
    8,578

    Default Re: Draining 2GM 20

    It's not necessary to remove a hose to change the impeller, there's sufficient play in them to twist the pump round once you've undone the mounting bolts. (Mounting the pump facing backwards is a poor bit of design IMHO)

  9. #9
    Join Date
    May 2001
    Location
    North Wales, sailing Aegean Sea or Menai Strait
    Posts
    21,453

    Default Re: Draining 2GM 20

    Quote Originally Posted by ghostlymoron View Post
    It's not necessary to remove a hose to change the impeller, there's sufficient play in them to twist the pump round once you've undone the mounting bolts. (Mounting the pump facing backwards is a poor bit of design IMHO)
    On my 3GM you are correct, it is possible to remove the screws and front plate without removing a hose. But it is so much easier if you also remove the discharge hose, a matter of 30 seconds. I agree about the design but it does make the installation more compact compared with the YM.
    Answers to some technical queries at new website http://coxeng.co.uk

  10. #10
    Join Date
    Apr 2005
    Location
    Shropshire
    Posts
    8,578

    Default Re: Draining 2GM 20

    I wasn't suggesting removing the screws with the pump in situ (that would be very difficult). But it's easy and quick to remove the pump mounting bolts then physically twist the pump body so that the face plate is towards you before removing the screws, plate and impeller.

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