Hot alternator on Mercruiser 5.7

Magic Dragon

Recruit
Joined
May 27, 2009
Messages
3
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.
 

flargin

Chief Petty Officer
Joined
Aug 13, 2008
Messages
540
Re: Hot alternator on Mercruiser 5.7

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? :confused:
 

Bondo

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Staff member
Joined
Apr 17, 2002
Messages
70,465
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...
 

Magic Dragon

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Joined
May 27, 2009
Messages
3
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.
 

APPALOOSA2

Petty Officer 1st Class
Joined
Jul 9, 2008
Messages
354
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.
 

flargin

Chief Petty Officer
Joined
Aug 13, 2008
Messages
540
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.

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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