Alternator/voltage issue on my 87,5.7 ltr mercruiser.

[Lwarden]

On my 87 5.7 ltr mercruiser the voltage gauge in the dash will intermittently peg at 16 volts. When this happens I can hear the alternator whine. When its not whining its reading 12.9 volts at the dash gauge but when its pegged and I take a voltage reading at the batteries its 17.9 volts. With everything off and the engine not running the batteries read 14.8 volts. It does this intermittently, so Ive checked all the ground wires for tightness and Ive wiggled every wire I can get my hands on to try to duplicate this symptom to no avail. Im wondering if the voltage regulator is going bad in the alternator? and if it is can you just change the regulator on the back of the alternator or do I need to buy a whole new alternator?

 

[theoldwizard1]

Likely the regulator.

On automotive alternators with built in regulators it is easy to change just the regulator. Don't know about marine, It depends on the manufacturer. Use yp.com to find an alternator rebuild shop in your area.

 

[Lwarden]

Do you really want a rebuild on a boat?? Ive always heard to go new???

 

[DaveG55]

Somethings I would only want new but an alternator is not one of them.
An alternator rebuild is easy to do. A few screws/bolts gets it apart. You put in new bearings, brushes and a new regulator and reassemble. The armature and stator are non wear items 99% of the time. An ohm meter check will confirm if they are good. The rebuild kits are usually under $100. I intend to rebuild mine myself over the winter.