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  1. #1

    Question Hot alternator on Mercruiser 5.7

    Can anyone help please? The alternator failed on my Merc 5.7 (2003/4). Next morning it was found to be very hot after an overnight stop. Yard replaced it, but after about 4 hours use (2 cruises) it seems to have burnt through the drive belt. Fitted new drive belt, 10 mins running and the new alternator is now very hot. The bearings are turning freely, so I suspect some kind of electrical fault on the boat. Any advice greatly appreciated.

  2. #2
    Chief Petty Officer Flargin's Avatar
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    Default Re: Hot alternator on Mercruiser 5.7

    Quote Originally Posted by Magic Dragon View Post
    Next morning it was found to be very hot after an overnight stop.
    does this mean that it was sitting, all night long, and it was hot in the morning, before running?

  3. #3
    Moderator Bondo's Avatar
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    Default Re: Hot alternator on Mercruiser 5.7

    Ayuh,... Sounds like you have a Dead Short somewhere, Inducing a Full Load condition on the Alt....

    Start unhooking systems til you find the Fault...
    Any Grease is Better,..... Than No Grease at All.......

  4. #4

    Default Re: Hot alternator on Mercruiser 5.7

    Yes Flargin, it was sitting all night, we used domestic items (lights, fridge) only, and it was hot in the morning before running. I had turned the ignition key for a moent, but as the battereis were flat the engine did not turn over.

  5. #5

    Default Re: Hot alternator on Mercruiser 5.7

    Quote Originally Posted by Bubba1235 View Post
    Have you checked the pully alignment with a straight edge? Eyeballing it is not good enough.
    Hi Bubba 1215; I will try to check pulley alignment, but it got hot whilst stationary.

  6. #6
    Petty Officer 1st Class APPALOOSA2's Avatar
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    Default Re: Hot alternator on Mercruiser 5.7

    Heck with alignment , just like Bondo said you have a serious Short !
    Start tracing back one at a time. I would suspect you should feel a warm wire to something with that much current being drawn.

  7. #7
    Chief Petty Officer Flargin's Avatar
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    Default Re: Hot alternator on Mercruiser 5.7

    Quote Originally Posted by APPALOOSA2 View Post
    Heck with alignment , just like Bondo said you have a serious Short !
    Start tracing back one at a time. I would suspect you should feel a warm wire to something with that much current being drawn.
    I would figure it out, or pull your battery why you are not working on it, and pull your shore power, if you have it. don't take any risks that the short will overheat..

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