260 Mercruiser Battery Problem

[JeighC]

I have a 1980 Cobalt with a 260 Mercruiser V8. This past summer I began having problems with battery maintaining charge while operating. I think the problem might be with the alternator, but someone else suggested a problem with the voltage regulator.<br /><br />The battery will take a charge when I hook it to a charger, indicating to me that the battery is good. <br /><br />The boat's amp meter moves slightly to the plus side when running, indicating to me that the alternator is putting out.<br /><br />However, after about an hour's run the engine will stall if I try to idle, and the battery is dead when I try to restart.<br /><br />I'm not a mechanic - the last engine I worked on successfully was the flat head V-8 in my 1949 Mercury in 1959! I recall from that experience that there was a generator and a separate voltage regulator. I understand now that alternators have built in voltage regulators.<br /><br />If the battery is good, and the alternator checks good, what should I check for then? <br /><br />Thanks - JeighC<br />

 

[Backlash]

Re: 260 Mercruiser Battery Problem

Hey JeighC,<br />You can check your alternator output easily enough with a VOM. It should be reading around 14 volts +/- at the battery with the motor running. If you've lost a cell in the battery, it won't hold a charge. Take your battery out & get it load tested....I think you'll find a new battery will solve your problem. <br />Backlash

 

[grandx]

Re: 260 Mercruiser Battery Problem

At full charge with a good quality Voltmeter, not the analog type on your boat. Your battery should have a voltage potential of about 13.6 volts. You can load test it yourself by cranking the engine, the starter motor is a good load, don't start the motor just turn it over like performing a compression test. I don't have my book in front of me, but after 8 seconds or so of cranking, your voltage should not drop below 12 volts if the battery is indeed good. If the battery loses excessive voltage from full charge. I would take it down and trade it in on a new one. Bring the battery to the battery shop again with a full charge and have them load test it again before you part with your money. Again, with a good voltmeter, with engine running your alternator should be putting out at 14 volts, to charge a battery you must supply higher potential to it, can't expect to get the 13.6 volts if alternator only putting out 13.5 volts. Good luck, <br /><br />Grandx

 

[JeighC]

Re: 260 Mercruiser Battery Problem

Thanks to both for the suggestion to check the battery. I did that earlier in the summer using a Simpson analog VOM, and it checked OK. <br /><br />The best test might be the suggestion to fully charge the battery, then have it checked at an auto parts store.<br /><br /><br />Jeigh<br />

 

[petryshyn]

Re: 260 Mercruiser Battery Problem

Sounds like a charging system problem. If the engine stalls after awhile, its because the charging system can't supply the demand of the ignition or fuel system. Take your voltmeter and measure the voltage at the battery while the engine is running. It should be atleast 13.8 volts. If its not that high, check the charging system for problems. Thats a whole different story...

 

[MrBill]

Re: 260 Mercruiser Battery Problem

JeighC:<br />Batteries are best checked with a hydrometer to determine condition. In your case however, it sounds like a charging system issue, and you'll probably isolate it to the voltage regulator which can be completely diagnosed on board with volt, ammeter and continuity test.