View Full Version : Possible alternator problem?

09-24-2004, 09:43 AM
I have a '93 Prostar 190 with 582 hours on it. The boat starts and runs fine, but when running the voltmeter reads less than 13 volts. I thought it should read 14.4V if the alternator is charging? I'm pretty sure the guage is working because the voltage dips when starting and if I turn on the nav lights or blower.

I purchased the boat this spring and it has been like this since I've owned it, about 70 hours. It has never failed to start or had any other problems.

The reason I bring this up is that I was out after dark for a while last night and had the lights on for a while. The voltmeter seemed to be reading a little lower than normal and it took an extra second or two of cranking to start.

What is the best way to test the alternator to see if it is bad? What is the typical lifespan of an alternator?

09-24-2004, 10:02 AM

The BEST way to test an alternator is to take it to an alternator rebuild shop and have them do it.
If your voltage stays at 13 or more, though, I wouldn't be worrying too much about it.

As far as lifespan goes, it's virtually impossible to say on a boat.. Moisture, not hours, is your biggest enemy. I've seen alternators on one-year old boats all corroded and starting to fail; on the other hand, I know of I/O's with over 15 years on the original alternator...

09-24-2004, 10:18 AM
Removing and taking in is the best way, but if you want to do a quick check, put a multimeter on the battery when the boat is NOT running, this reading should be around 12.55 to 12.70 volts. Now start the boat and take another reading, this should read 13.8 to 14.6 volts.

09-24-2004, 10:19 AM
I suppose that is what concerns me, I've never seen the voltmeter read at or above 13 volts. However, the boat starts and runs fine.

Is pulling it the only way to test it? I was hoping there was an easier way.

Thanks for the reply.

Edit: Didn't see Footin's reply. I'll take the multimeter with me next time I'm out. Thanks.

09-24-2004, 10:21 AM
Don't always trust the gauge. I had a 87 Prostar 190 that read 10 volts when not running; however the multimeter showed 12.65.

lakes Rick
09-24-2004, 11:00 AM
Brian, my 94 reads the same, around 13 volts.. I honestly do not think the stock gauges are the best..

09-24-2004, 01:48 PM
Thanks guys, it's reassuring to know that the guage could be the culprit.

I'll check the voltages with a multimeter next time out to make sure.

09-24-2004, 06:40 PM
All great information guys. Keep in mind too that if the battery is fully charged (12.68 v) the alternator will be not be putting out as much voltage. If you are reading 13.5 volts or less, turn on some lights and crank up that stereo then see what the old multimeter says. Should read 14.3 (+/- for the inaccuracy of the multimeter).

09-24-2004, 06:49 PM
95 PS205 LT1, My gauge sucks. It is even worse than yours. The alternator is only one year old and usually reads between 10 and 12. I put a multimeter on it and it reads just over 13.5 with heater and shower running. I hate not having one that I can rely on!! :mad:

09-24-2004, 07:16 PM
If you want to know how far off the gauge is and why, neasure the resistance from the ground on the gauge to the battery negative post, not battery neg cable. Clean the terminals after you measure it, then re-measure. If you see the voltage go up immediately after cleaning the terminals, you then know that they need to be cleaned more often. If it doesn't change and you see more than 1-1.5 ohms from the gauge neg to the battery neg post, check any connections between the two positions.

Brian- removing two wires and three bolts so the alternator can be taken in for testing hardly sounds like a big chore.

10-01-2004, 08:38 AM
I was able to take a mutlimeter out with me last night and take some measurements.

With the key off the voltage across the battery terminals is 12.56V. With the engine running the voltage is 14.1V. Looks like everything is fine.

Both battery terminals are clean and are solidly connected to the wires. From JimN's post above it looks like I probably have a poor connection somewhere in the path to the guage.

10-01-2004, 10:20 AM

It doesn't hurt to check to see if all of your electrical connections are clean, dry, tight, and corrosion free, but, most likely, the guage just isn't calibrated right. They are mass produced and aren't that accurate. The important thing is that now you know what "normal" is on the gauge -- if it varies from that, then something is wrong...

10-07-2004, 10:30 AM
The gauge on my 94 constantly reads between 10-11. I have assumed that the gauge is wrong since the engine starts strong every time (however, my batteries only last about 3 years, max.)?