Optimax: Battery Voltage Sags to 11.7-Volts at Idle

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Author Topic:   Optimax: Battery Voltage Sags to 11.7-Volts at Idle

Smithy UK posted 05-27-2008 02:23 PM ET (US)
I have an Optimax 225 which starts fine, but drops voltage when running. The Smartcraft display shows around 11.7volts on idle which drops when the engine revs are increased. A multimeter shows the voltage to be around 12.5v at idle, which drops when the revs are increased and then returns to 12.5v.
If I try to use the trim the battery warning beeper sounds and the engine slows down.
Also the engine misfires at high RPM, it seems to like running at 3000rpm. I have a new 800CCA battery located in the console which shows 12.6v at rest.
Do I need a bigger 1000CCA battery or is it likely the alternator is not producing a charge?
Any help gratefully received.

Lars Simonsen posted 05-27-2008 08:42 PM ET (US)
The 1000 cca battery is the minimum size for these motors, so if you have anything less, you should get a proper battery. However, the symptoms you describe are similar to the symptoms I had when my alternator was dying. One of the first symptoms is that I'd be running along, and then the motor would seem to bog down, then start running fine again.
I don't have a Mercury mechanic nearby (closest one is a 45 minute drive one way), so I took off my alternator and brought it to a car parts store for them to test it. Sure enough, it was bad.
Prepare for sticker shock on the alternator (assuming you can find one). On my 1998 Optimax 135, the alternator cost over $500.00. It was difficult to find, as it is a discontinued part. I kept the old alternator, as it is an automotive unit (I think it's made by nippondenso), and I suspect it could be rebuilt at any decent rebuilder's shop.
glen e posted 05-27-2008 08:48 PM ET (US)
[H]is batt[ery] is fine. [Mercury OptiMax motors] need [a cranking battery with a rating of] 800-CCA or 1000-MCA. He does not need 1,000-CCA. See page 12:
http://northamerica.mercurymarine.com/_media/pdfs/serviceandwarranty/maintenance/MaintenanceInformation-OptiMax.pdf
[Your problem] is the alternator.
Clyde posted 05-27-2008 09:05 PM ET (US)
I had similar a similar problem on my 1998 135 optimax. Turned out to be the alternator. New the sticker was $750cdn. I had mine rebuilt far $210 at a starter re-builder. Works fine five years later. The interesting thing was that the shop said that the inside of the alternator had loose screws and bolts which they thought probably were that way from the factory. It had basically self destructed inside.
FWIW.

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Author	Topic: Optimax: Battery Voltage Sags to 11.7-Volts at Idle
Smithy UK	posted 05-27-2008 02:23 PM ET (US) I have an Optimax 225 which starts fine, but drops voltage when running. The Smartcraft display shows around 11.7volts on idle which drops when the engine revs are increased. A multimeter shows the voltage to be around 12.5v at idle, which drops when the revs are increased and then returns to 12.5v. If I try to use the trim the battery warning beeper sounds and the engine slows down. Also the engine misfires at high RPM, it seems to like running at 3000rpm. I have a new 800CCA battery located in the console which shows 12.6v at rest. Do I need a bigger 1000CCA battery or is it likely the alternator is not producing a charge? Any help gratefully received.
Lars Simonsen	posted 05-27-2008 08:42 PM ET (US) The 1000 cca battery is the minimum size for these motors, so if you have anything less, you should get a proper battery. However, the symptoms you describe are similar to the symptoms I had when my alternator was dying. One of the first symptoms is that I'd be running along, and then the motor would seem to bog down, then start running fine again. I don't have a Mercury mechanic nearby (closest one is a 45 minute drive one way), so I took off my alternator and brought it to a car parts store for them to test it. Sure enough, it was bad. Prepare for sticker shock on the alternator (assuming you can find one). On my 1998 Optimax 135, the alternator cost over $500.00. It was difficult to find, as it is a discontinued part. I kept the old alternator, as it is an automotive unit (I think it's made by nippondenso), and I suspect it could be rebuilt at any decent rebuilder's shop.
glen e	posted 05-27-2008 08:48 PM ET (US) [H]is batt[ery] is fine. [Mercury OptiMax motors] need [a cranking battery with a rating of] 800-CCA or 1000-MCA. He does not need 1,000-CCA. See page 12: http://northamerica.mercurymarine.com/_media/pdfs/serviceandwarranty/maintenance/MaintenanceInformation-OptiMax.pdf [Your problem] is the alternator.
Clyde	posted 05-27-2008 09:05 PM ET (US) I had similar a similar problem on my 1998 135 optimax. Turned out to be the alternator. New the sticker was $750cdn. I had mine rebuilt far $210 at a starter re-builder. Works fine five years later. The interesting thing was that the shop said that the inside of the alternator had loose screws and bolts which they thought probably were that way from the factory. It had basically self destructed inside. FWIW.