Charging problem on malibu with hammerhead engine

I have a 2001 malibu response lx with the hammerhead engine. For some reason our battery isn't charging right. When we put the boat in the water, the battery seems to be charging just fine (12.5 on PP and over 13 on the gauge). After riding all day, the voltage drops to about 11.9 on PP and under 12 on the gauge. We have a fairly new blue top optima battery, so I dont think the battery is bad. Is it possible that our alternator stops working after it gets hot, possibly a bad alternator? I have checked all the connections on the battery, and I have sanded off the terminals on the alternator to make sure of a solid connection. Any other thoughts on what it could be. I forgot to mention that the stereo is unplugged and we don't use any accessories while running the boat to help troubleshoot the problem.

I would definietely have your Alternator looked at. It sounds like that us the issue.

Your alternator should be at 13.8 when running, and could be up to 14.5

Art-the gauge reads a little under 14 (so about 13.8). I was told that Perfect Pass gives a reading that is about 1 volt less than actual reading. I took my alternator to a testing center and everything read fine. Is it possible that the alternator isn't working properly when it gets hot? I only notice the charging issues after riding for a while.

All alternators work less efficiantly when hot. That is the time to test them. Use a DVOM = Digital Volt Ohm Meter and measure it at the battery and at the alternator. The spec is 13.7-14.3 volts. With a load it may drop at idle, but if revved slightly it should jump up. Try loading it with all the accessories and see if it changes much.

Often gauges are hooked onto a circuit that is not large enough to carry all the amperage load from different components. Only trust a direct connection.

Is the battery going dead?

Peter-I don't think it is the battery, unless the battery starts to drain the longer it is used. We bought the battery last summer. I have an extra blue top optima I can experiment with.

With a load, the engine voltage drops even more (around 11.5 on PP).

Also, when first start the engine. It charges up just fine. It is after we run for a while that the voltage goes down.

(Message edited by malibuboarder75 on June 21, 2007)

Leo, who did you have test it? Is it the original alternator? Haev a reputable shop test it, not Auto Zone, ect. Did this problem just start?

I had a simialr problem...ended up being a bad regulator in the alternator. the regulator was nto bad but going out adn woudl work for abto the first two hours out then not work. I coudl soemtimes hit the alternator a few times adn it would work for 15-30 min then go out again (no voltage) untill finally it went bad.

I had carquest check it. Our only reputable alternator shop couldn't test it because their machine was broken. Carquest didn't even know how to test it. I had to go back to the alternator shop to get instructions on what to do. The test showed that it was getting good amperage and voltage.

Thanks Adam. I'll keep running the boat a few more days. If it keeps charging at the beginning of the day, then dying, I will suspect it is the alternator.