bad altenator?

[randy becraft]

hi new to this forum.voltage meter shows 13+ at idle, but drops when i rev it up .its a 1997 mercruiser 5.7 with a mando altenator...replaced the altenator with a used one from a frind and it does the same.any thoughts? thanks randy

 

[jlinder]

Re: bad altenator?

Assume you are reading tihs on a dash mounted volt meter.<br /><br />It may be possible that what you have is a faulty reading. You need to get a digital voltmeter and read it at the battery.<br /><br />Let us know

 

[randy becraft]

Re: bad altenator?

checked at battery with voltmeter .had to jump start first... with engine running the voltmeter read around 14.84-14.88and up to 15+ when engine was reved...yet dash gage moved from below 13-maybe 13+ and backto below 13 volts. all the while my volt meter read 14+ unless i played with the trim... with engine off and meter still hooked up battery volts read 13+ but started to fall as i watched.after five minutes the volts were down to 12.55 and engine wouldnt crank over enough to start . bad gauge? and battery? thanks

 

[randy becraft]

Re: bad altenator?

oh, forgot to mention that i jumped engine off, and after running for three or four minutes shut it off,let sit for a few moments and it would start fine. but after five or ten minutes it failed to restart. dead cell maybe? thanks for all your advice...randy

 

[schwahn]

Re: bad altenator?

I'm guessing you have a bad battery (as you pointed out)which from experience with a car will destroy your alternator fairly quick (went through three of them on a car in a month before someone suggested that the batttery may be shot. Replaced battery and alternator run fine)!

 

[randy becraft]

Re: bad altenator?

thanks.. ill try that first...