4.3LX Mercruiser Questions/Fixes

[chriswh86]

Hi all,

I recently had a 90' campion allante 185 w/ 4.3LX mercruiser motor inspected.

The inspector found the following issues.

Charging system seems to be running at about 11.5v at idle and drops to a little above 10volts when trottling up to 2000rpm. He figures it will need a new alternator or batteries. Im looking for clarification on this.

Also, these are the specs he got from idling the engine...

Warm engine
40psi oil pressure
temp 130 degrees
800rpm at idle

Im looking for what people can tell me on the charging system, how easy is it to do, what the actual issue may be and what parts might need replacing.

Id also like to see if the engine specs at warm idle sound good.


Chris,

 

[dubs283]

Re: 4.3LX Mercruiser Questions/Fixes

sounds okay, 800 rpm is a little high for idle speed, should be more like 650-700 in gear

replace/rebuild the alternator, that is the cause of your charging system issue

 

[chriswh86]

Re: 4.3LX Mercruiser Questions/Fixes

Thanks for the reply Dubs,

What are the chances the batteries are low on charge or dying? They have been sitting for a bit...

 

[Trooper583]

Re: 4.3LX Mercruiser Questions/Fixes

I believe that your volt meter should still be reading in the 12.5 - 13 volt range whether or not the batteries are properly charged. In fact, if the alternator were charging the batteries it should defintely be higher than 11. At least my 4.3 LX does. If I had to guess I'd say it's the alternator. I would try to get it rebuilt, that would be much cheaper than buying a replacement.

 

[Trooper583]

Re: 4.3LX Mercruiser Questions/Fixes

Also, if you really want to rule out the batteries, take them to a parts store. They will be able to test them and tell you what the voltage and cranking amps are for that battery.

 

[chriswh86]

Re: 4.3LX Mercruiser Questions/Fixes

Is there any write ups on alternator rebuilds for the merc?

 

[Pete104]

Re: 4.3LX Mercruiser Questions/Fixes

Is this the only thing you found wrong with this boat?

 

[chriswh86]

Re: 4.3LX Mercruiser Questions/Fixes

couple other small things but not related to charging/elec system

 

[Pete104]

Re: 4.3LX Mercruiser Questions/Fixes

Take the alternator to a repair shop & have them go thru it. Probably about a hundred bucks if it doesn't need a reg.

 

[chriswh86]

Re: 4.3LX Mercruiser Questions/Fixes

better off to buy a rebuild alt if the regulator is screwed?

 

[Pete104]

Re: 4.3LX Mercruiser Questions/Fixes

Yes.

 

[MarkySparky]

Re: 4.3LX Mercruiser Questions/Fixes

Hey Trooper583 and others,
If it were bad batteries, the alternator would probably be trying harder to charge them. A quick and dirty way to check the alternator output is to touch the rear bearing cap on the alternator with a wrench or screwdriver while engine is running. Be careful not to short out to output terminal of alternator. It should be fairly strong magnetic attraction. If alternator is weak (usually diodes going bad) magnetism will be weak. If no magnetism (like same as when engine is off), alternator regulator may be the culprit. Also, check battery connections, terminals should be shiny silver cleaned. Alternators and batteries are both expensive, so get a proper test done if in doubt- don't just guess and throw parts at the problem. Alternators are pretty easy and inexpensive to rebuild (parts available at any auto parts store) and batteries are often just low on water or corroded terminals (often shiny black). Even "maintenance-free" batteries often can be topped off with water. BTW, dashboard voltmeters are often inaccurate so don't depend solely on them for troubleshooting. Just my 2 cents, from a retired US Navy Seabees/Naval Coastal Warfare Construction Electrician. Go Navy!