View Full Version : Alternator or Serpentine belt

06-26-2011, 09:59 AM
When I put the boat in the water this year I bought 2 new batteries and the boat ran fine. After using it 2 days and letting it sit for a week both batteries were dead. I jumped it and ran for a half hour and the batteries had no charge. I noticed the amp reading would fluctuate from just under 13v to 10v while driving. The boat runs fine but the batteries weren't charging , I noticed the belt was squeeking so I tighted it up and after running a while the batteries picked up a little charge but the belt is still squeeking and it still drops to 10v while running at 3k rpm.

I have ordered a new belt but does anyone know how to tell if it is simply the belt or the alternator.

I put a new alternator in last year...

2004 X star with an Indmar engine


06-26-2011, 01:15 PM
Check all connections for tightness. Use a voltmeter to check amperage off the alternator. Sounds like something else is loose or on draining your batteries if the boat sat for a week and drained 2 of them. I'm pretty sure a bad alternator won't drain the battery when the engine's off. Also may want to pull the batteries, charge them, and see if they hold. May have gotten a bad one.

06-26-2011, 01:42 PM
There was a problem in 2004 on the altinator bracket, I would check to see if one of the mounting bolts are snapped off cause the altinator to be slightly off line. This happened on mine, indmar has a updated bracket and bolt setup for this.

06-26-2011, 06:27 PM
Turn the key on and see what the volt meter reads. It should be about 12v. Then fire it up and it should read about 2 volts more at idle. If it does not go up, the alternator is likely fried.
If the volts go up and down irratically, then its the alternator, or a loose wire/bad connection.

Its not uncommon for an alternator to stop working after 1 year. Sometime you get several years out if them, somtimes you get a few days.

06-26-2011, 11:58 PM
Thanks I will try these ideas tomorrow and see if I can figure it out.. I did not check the wires so that may be it.


06-30-2011, 10:45 AM
Ok, so I checked all the wires I could think of, the battery, the battery switch, the alternator and could not find any loose. I put a new serpentine belt and alternator and when the boat fired up the volt meter showed a little more than 13V. I ran the boat for a half hour and it ran fine, I was hoping it was charging up the batteries which had drained dead (both batteries are brand new) and when I put it in idle the volts dropped below 12 volts and the Batt came on in the perf pass screen and the screeching alarm went off.

when I raise the rpm the volts go back up to 13 and the alarm goes off but when I go to idle it drops to below 12. I also noticed that at running the volt meter was slightly less than 13, when I first started it the volts were slightly more than 13.

I went back to the dock, shut it off and the boat would not start, apparently it had not given any charge to the batteries.

I am at a loss , Any ideas what to do next ?
Of course I could have bought a defective alternator, or 2 defective batteries, but not likely

What other wires should I check, what about the switch that turns off battery 1, 2 or both
I would think if that went it would not vary the voltage on the volt meter.

2004 x star, Indmar engine.



06-30-2011, 10:47 AM
take the batteries to auto zone and get them tested

06-30-2011, 11:55 AM
That is a good idea.. they are dead anyway so I should charge them up. I don't think that is the root problem, both batteries are brand new but it will eliminate one more thing.


07-09-2011, 12:13 AM
Ok, I cleaned all the terminals and then ran a voltmeter from the alternator to the battery. I am getting 13.5 volts at the alternator but that drops to approximately 12 at the battery isolator. It looks like I lose a volt from the wire that comes to the alternator to the wires that go off the isolator to the batteries. I took the wire from the alternator and connected it directly to one of the leads at for the battery and I get over 13 volts at the battery. I drove the boat and it looks like it maintains the voltage and started to charge the battery. I found a new Guest battery isolator online and ordered it for $40. It should be in next week, I think that will do it.