Weird Charging system issue, Im stumped

Hello, So my friend and I took his boat out on Lake erie today and had a strange issue that I hope that you cant help me with. First, Ill start with Im brand new here and I live in Michigan. My Friend has a 26ft Cruisers inc with a 454 magnum mercruiser and an Alpha 1 drive.
So last year, The last ride of the year as we came back to the launch the alternator quit working on us. All year charging seemed very low. One of his batterys was bad so we that maybe that was the issue. So we got the boat to his place winterized it and didnt work on it until this spring. So he went and bought a new 4 wire Prestolite style alt. As I almost get the bad starter out i notice that the Exciter(purple) wire came loose and disconnected(was a little black at the end). So we decided to hook the old alternator back up and see if was accually bad of not. we discovered that I wasnt so we kept the old alt on and took the new one back..........

Today we got the boat out for the first time this year. Started and run perfect the entire from the launch and out the channel. So we get out on to the lake about a mile and we are losing charge again. Stopped the boat, checked all connections to both battery and alternator..... nothing is loose or disconnected(and by the way, the alternator was very hot). Only thing we see is that the engine is wet. As Im trying to figure this out I notice that there is a very very very small pin hole leak coming from the front of the waterpump and hit the back of the pulley. It wasnt bad at all, but we discover that when the boat is running there is a constint mist in the engine bay and everything is getting wet(which answered why the engine was wet earlier) Barely get the boat restarted and try to get back to launch asap. we both noticed that at 11.9 volts we didnt loose anymore charge until we used the trim or drive hydraulics. When using extra power wed loose it but when not using any extra the voltage held steady. So we get the boat home, charge the batterys and start up the boat to check the voltage at the battery and at the alternator. Before we even test the alternator the voltage gauge is going back up and everything is working again............

So my question is if the alternator gets to wet, will is stop working and work again when is dries out. Or could maybe from the exciter wire being loose last year maybe the voltage regulator was damaged and get to hot to work and shorts? Idk any info would be very helpful

Altenator may be bad and all power is supplied from your new battery. The battery is being drained over time with not out bieng charged by the alt. An alt getting hot is not because it is still good. Alt's are really current generators and having an open circuit will burn it up. Never disconnect wires from an alt while the engine is running. Diodes immediately burn up. They short first, (get hot), then burn open.

I forgot to mention that both the batteries are brand new this year. I heard that the water could have gotten in the alternator and basicly coated brushes and make the alternator not work correcrly and after wer got it home and it dried out it started working again. Does that sound possible.

Going to get the water pump in about an hour

Marine alternators are not sealed....they are "screened" so any spark is arrested to the screen which acts like a ground path.

Second if the water was spraying and it got the belt wet enough it could have been slipping. This might explain the hot alt, did you find any black sooty material around the pully?

Also if you are going to replace the alt, replace it with a OEM if possible. A bit more expensive but they work!! Mine went out after 20 something years and I bought a brand new one from Merc. If the original last 20 something years that tells me that is what I want when I replace it.


If you don't want to buy new have the merc alt rebuilt... 1/2 cost.

As far as your issue. a static battery (no connections) fully charged should be ~ 12.7 volts not higher but possible .2 to .3 volts lower. If a static battery fully charged is below 12 volts you have a bad cell.

When connected and engine rpm is 1500 - 2000 the charge voltage should be min 13.4 and max 15 vdc. Typical average is 14 vdc and after initial start it may drop lower as the battery charges back up.

So if you are running and the charging voltage drops below 13 you have a problem. If both batteries are good and you know this to be true and one is not bad taking the other one down with it... then the alt is no good and needs replacement or rebuild.... The fact that there was a loose connection that got crispy could have done some damage...

Also if you are using one 65 amp to charge two batteries you may want to change the orange wire from output of alt to starter post from the 10 gage to 6 gage... having two batteries simply connected together can allow the alt to charge at a higher amperage for longer periods of time.

I have three batteries running thru a isolator, cranking battery from one leg of isolator and the other two batteries off the other leg of the isolator, I have changed the alt output wire to a 4 gage battery cable.. The alt tends to output more amperage with multiple batteries.

if it was my boat, I would fix the water pump leak, check and clean all cables and connections and dry it out for a day or two. Then fire it up and measure the voltage going to the battery, should be a minimum 14 volts I believe. If it is reading well, your done. Don't go replacing ANYTHING until you have diagnosed the problem. My pet peeve is all these posters saying replace this and replace that. Makes no sense.

philipp10 said:

Don't go replacing ANYTHING until you have diagnosed the problem. My pet peeve is all these posters saying replace this and replace that. Makes no sense.

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So what is your point????

And who are you referring to "all these posters"?

kghost said:

So what is your point????

And who are you referring to "all these posters"?

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not necessarily you. But there are a lot of people on these sites that act like everytime there is a problem that they should just start replacing parts. Until they are proven bad, what is the point of replacing anything? Just saying. I believe I was referring to some earlier posts on a different subject where there were a lot of "part replacers" there. Just saying.

I came across such a thing last weekend

An acquaintance of mine showed up with his alpha one gen II outdrive complaining that when turning he could hear a grumbling to knocking sound.

He thought he knew/knows a lot about his boat(s) so he decided to replace the gimbal bearing and purchased two new ujoints and needed me to help replace them as I have all the tools needed to disassemble and reassemble the upper gear case to gain full access to the ujoints.

So we replaced a perfectly good set of ujoints and he said the gimbal bearing did not solve the issue so that was replaced for no reason also.

In the end when I spoke with him a day later he confessed up as to what was really going on.


His trim gage has stopped working, Bad sender/broken wires.

When he trims his outdrive up in shallow water he has no idea where it is and that is when the noise is heard.............


Duh........all outdrives make noise when trimmed way up and under power and turning...........

Lesson learned I hope on his part.............

kghost said:

I came across such a thing last weekend

An acquaintance of mine showed up with his alpha one gen II outdrive complaining that when turning he could hear a grumbling to knocking sound.

He thought he knew/knows a lot about his boat(s) so he decided to replace the gimbal bearing and purchased two new ujoints and needed me to help replace them as I have all the tools needed to disassemble and reassemble the upper gear case to gain full access to the ujoints.

So we replaced a perfectly good set of ujoints and he said the gimbal bearing did not solve the issue so that was replaced for no reason also.

In the end when I spoke with him a day later he confessed up as to what was really going on.


His trim gage has stopped working, Bad sender/broken wires.

When he trims his outdrive up in shallow water he has no idea where it is and that is when the noise is heard.............


Duh........all outdrives make noise when trimmed way up and under power and turning...........

Lesson learned I hope on his part.............

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it happens. Hopefully we learn from it. I find the older I get the better I am at stopping and thinking things thru first. But I have done plenty of home restoration projects twice because I didn't like how they turned out the first time I did them...lol

philipp10 said:

not necessarily you. But there are a lot of people on these sites that act like everytime there is a problem that they should just start replacing parts. Until they are proven bad, what is the point of replacing anything?

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Regardless of who you were refering to...., I certainly agree with you. All too often diagnostics are not done properly.
That said, I do believe that some parts that are considered to be "wear items" should be replaced routinely.

My suggestion is to use the tried and proven P of E..... (process of elimination).
Check/test one item and one item at a time ONLY.
When used methodically and systematically, the P of E won't let you down.


Otherwise, you can toss parts at a problem all day long, and you will eventually correct it.... but you may never know what the issue was to begin with.


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