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  1. #1
    Cadet
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    Default How to know if water pump impeller is working?

    How does one tell if the water pump impeller in the lower unit is bad? This is a 1981 mercruiser 120. Outboards have the telltale pee hole but I've never heard of how to know if it's working on an I/O.Thanks,Joe

  2. #2
    Petty Officer 2nd Class
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    Default Re: How to know if water pump impeller is working?

    do you have a temp gauge?

  3. #3
    Petty Officer 1st Class
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    Default Re: How to know if water pump impeller is working?

    As blackz3 says, high temperature reading would mean that impeller replacement may be needed.If it is older then 2 years old, replace it. If you do not know how old it is, replace it. It is a pretty simple thing to do it yourself. I change mine every year during the winter. This way I know for sure I will not have to worry about it when the season starts. Good luck!

  4. #4
    Petty Officer 1st Class
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    Default Re: How to know if water pump impeller is working?

    I would say if your over 170 consistantly, replace it. Mine goes up to about 165 170, then cools to 160. Don't let it overheat.....

  5. #5
    Lieutenant Commander flashback's Avatar
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    Default Re: How to know if water pump impeller is working?

    Yep, thats about it, until you have it in your hand, you won't know. But high temps are a good indication.. if you run it for 10 mins. and can lay your hand on the exhaust manifold without getting burned, the pump is probably OK...
    The Devil to pay, and no pitch hot!

  6. #6
    Cadet
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    Default Re: How to know if water pump impeller is working?

    Thanks guys, I know I could watch the guage but thought there may be some telltale way to know if it's working as soon as I have it running. I just got the boat so don't know how old the impeller is so I suppose I'll just replace it. Is it necessary to get the kit with gaskets and wear plate or is only an impeller usually all thats needed?

  7. #7
    Lieutenant Junior Grade jlinder's Avatar
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    Atlanta GA
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    Default Re: How to know if water pump impeller is working?

    Mine is pretty simple to change out (OMC cobra). If yours is, just pull and check it out.

  8. #8
    Honorary Moderator Emeritus Don S's Avatar
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    Aug 2004
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    Western WA.
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    Default Re: How to know if water pump impeller is working?

    Get the gaskets. NEVER reuse old gaskets or you will end up with an overheat problem when the suck air instead of water.And NO it isn't as easy to change as a Cobra.
    Don S.


    Please, no PM's (Private Messages) regarding boat/engine problems.
    That is what the forums are for.
    Only forum/moderator issues will be answered in PM's.

  9. #9
    Chief Petty Officer
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    Mar 2005
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    canada
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    623

    Default Re: How to know if water pump impeller is working?

    remove water in hose to thermostat housing start motor at idle it should have about a 6" head of water

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