Alternator?? Battery?? 2008 Supra Launch 20 Indamar 325

So a couple weeks back I had a problem with my boat running over the battery threshold 17.6 or so. This was not normal so I went to a supra dealer and they had an alternator. I replaced it on site and cranked her up. She started and seemed to run fine. The volt meter showed both batteries around 14.0 at idle. I did not get a chance to go out on the water until yesterday (3 weeks later) . I started her once a week just to keep her running. I kept my eye on the volts via dash board and they showed around 14.0-14.3.

9/6/2014 (Saturday)
When I got out on the water as I was leaving the boat ramp just coasting in the no wake zone, the boat still read 14.0 volts. As soon as I got to the spot I was going to ski at I saw a threshold warning and saw the volts were at 11.5. I road for a little while and the voltage slowly started to creep down so I came back in. Made it back and the boat said 10.9 at this point! Something is not right.

9/7/2014 (Sunday)
I took both batteries out of the boat and charged them over night. Brought both batteries to advanced auto parts to get them to test them out. One was good and one was bad. So I replaced one of them and installed them back in the boat. I started the boat back up and the dash read 11.6 volts and the Threshold warning was back!!

I turned the boat off and charged the older battery of the two for a couple hours and checked both of them with a volt meter after. Both read about 13.0. I started the boat up and they both read 12.67-12.7 at idle. I had someone get the RPM's up as I watched the volts on both batteries and they did not rise. they actually dropped some not much but some. While I watched the volts with the volt meter the dash read 11.7 which was off some. When I turned the boat off I checked the batteries again and they read 12.67.



So now I am trying to figure out my next step. I replaced the alternator and both batteries. But it seems like the alternator is bad. Maybe it was a rebuilt one or maybe something else. Any suggestions anyone? The alternator cost 300.00 so I would expect it to work perfectly!


Thank you for the responses in advance!

You need to check the reference into the alternator and the charge voltage out of the alternator, right at the alternator. Sure sounds as if the alternator is not charging is not charging, but may not be the alternator.

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Originally Posted by Wylietunes

You need to check the reference into the alternator and the charge voltage out of the alternator, right at the alternator. Sure sounds as if the alternator is not charging is not charging, but may not be the alternator.

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Thanks man, much appreciated for you thoughts!! But if it isnt the alternator and it isnt the battery what do you think?

Are you checking voltage with a separate volt meter or just the dash gauge?

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Originally Posted by Suprawake42

Thanks man, much appreciated for you thoughts!! But if it isnt the alternator and it isnt the battery what do you think?

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I sounds like the new alternator went bad. The "what else" would be that the shop did not tighten the alternator connection and it came loose.

A bad cable or a loose or corroded connection can cause a perfectly good alternator to not charge the batteries. With the engine running, take a volt meter and start at the battery and work backwards until the point of the voltage lose is found. Dont overlook the ground cables. They are 50% of the electrical circuit.

Sounds good Mike!

I am going to check the cables connected to the alternator and make sure they are secure and that there is no corrosion that could interfere. So should i take the volt meter to the positive and negative posts on the alternator as well?

A loose connection can be found with a simple wiggle, but the meter will allow you to "see" inside that cable for corrosion that the naked eye will never find. The alternator is grounded to the block, so check the main ground cable from the battery, as thats the one that completes the circuit.

Just an update. As I was going to check the alternator I noticed my belt was broken. I guess the boat will still run without the belt until the battery dies! Would you all conclude that to be true?

I have an Indamar Assault 325 in my 2008 Supra. Just in case anyone with the same engine needs the serial number it is : 143631.

The belt part number is: 725018.

Thats would be accurate, engine will run until the fuel pressure drops, ignition output falls off or the ECM just shuts down, due to dropping voltage.

Check to make sure the alt will spin freely. next, I would check the alignment, especially if its a multi-grove belt.