charging/alternator issue for 3.0L Mercruiser

[barryboy70]

I have a '91 Maxum 1900 SL boat with a 3.0L Mercruiser inboard. Engine has very low miles and other then replacing the starter the week I bought it, I have had no problems.<br /><br />Today I went out and it seems that the battery is not charging. Alternator I suspect...<br /><br />1) Is there a simple way a non-mechanical guy can test the alternator to see if its functioning properly?<br /><br />2) Other than the alternator, are there other components of the charging system I should look to for a source of the problem?

 

[DJ]

Re: charging/alternator issue for 3.0L Mercruiser

Barry,<br /><br />Put a volt meter across the battery terminals. Multi function meters can be had for $10.00-$15.00. Start the engine. It should read well above 12.5 volts with the engine running.<br /><br />You could have alternator or voltage regulator troubles. I'm not sure if your alt. has an internal regulator, or not.

 

[denniz]

Re: charging/alternator issue for 3.0L Mercruiser

OR If its not a computer controlled engine,and a 3.0 is not. pull your positive cable loose. If your alternator IS putting out it will stay running if not it will die.

 

[Ralph 123]

Re: charging/alternator issue for 3.0L Mercruiser

Rod,<br /><br />Doesn't that risk destroying the altenator by destroying the diodes since the voltage rises quickly above the limits of the diodes without the load of the battery? Isn't that what Zap-Stop Alternator Protectors are all about?<br /><br />Barry<br /><br />You can also take your battery to a place like Autozone and have it tested. If it tests good it's your alt.

 

[Trent]

Re: charging/alternator issue for 3.0L Mercruiser

I have to agree with Ralph...That is really a trick from the old days with generators. I know it works sometimes, But you risk the diodes in the alternator when you do that. Djohns has it right. Use the voltmeter to check 12.5 is a normally charged battery. When you crank and run the engine it should be above 13.5 volts.<br /><br />Depends on the alternator you have. You could just have a regulator problem. Regulator faulty.....no charging.

 

[Boatist]

Re: charging/alternator issue for 3.0L Mercruiser

I also agree with Ralph. Not worth the risk. In fact a loose battery cable one of the main causes of blown alternator diodes. If you have a voltmeter on your dash then check voltage before you start it and then again after you start it.<br /><br />A charged 12 volt battery should read 12.6 volts or more and while charging with a I/O alternator voltage should be 13.8 to 14.8 volts. Check the alternator drive belt and make sure it is snug. After that time to check the voltage regulator and alternator diodes.