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  1. #1

    Default Merc 2.5 HP 2 Stroke Cooling Problems

    Recently bought this second hand motor, (S/N 0D918709) and starts up fine. Cooling discharge rate seems to be extremely low at only a steady drip drip rate increases slightly with motor speed but never achieves a steady stream. Replaced water pump impeller and ensured the clear discharge line coming from the engine block is unblocked. Is there anything else I should be checking before digging deeper into the power head and lower unit's water tube?

    Also, the manual I have indicates that there is a seal and spring assembly supporting the water pump impeller. I did not see either of these when replacing the impeller. Any suggestions appreciated. Thanks.

  2. #2
    Join Date
    Sep 2010

    Default Re: Merc 2.5 HP 2 Stroke Cooling Problems

    Are you testing this on a boat or on a stand / bucket / 45 gallon drum ??

  3. #3

    Default Re: Merc 2.5 HP 2 Stroke Cooling Problems

    I've found that the small, made by Tohatsu, 2-strokes with weak
    cooling water flow can frequently be fixed with a shot of compressed
    air into the rubber discharge hose. If you don't have an air compressor,
    a can of "Dust Off" will work. Just make sure you have a good seal
    with the hose and give it a couple of shots.

    More info can be found on this website...in the Tohatsu section.

  4. #4

    Default Re: Merc 2.5 HP 2 Stroke Cooling Problems

    Thanks very much for responding to my post.

    I have seen this both on the boat (inflatable) this summer and most recently on a stand with the motor's lower unit submerged in a large water filled trash can. Why would this make a difference? Thanks again, Dave

  5. #5

    Default Re: Merc 2.5 HP 2 Stroke Cooling Problems

    Thanks,whitegreg56, I will give the dust off a try and after reading the through the Tohatsu section will also try clearing out the discharge line while the engine is running.

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