Engine dies....on time

Rivertender

Rivertender

Member
Nov 7, 2006
123
Tampa Bay
Boat Info
370 aft cabin S Ray 1997
Engines
Twin 454
Inboard
Hoping you all have a thought or 2 on my what appears to me to be.......an altetnator issue:

2 inboards
Both start nicely

20 mins run time or so and the port motor dies...dependably time wise. No gasping or choking- just shuts down.

Using emergency start, the port engine will then turn over nicely- even start for a moment- then shuts down as soon as the emergency start is released

Immediately after engine shut down, in the slip, charger shows putting 40 plus amps out to charge up the system....she's working hard using shore power.

My guess, I am thinking the alternator is not putting out-- the shore power is however topping the battery off- port engine starts beautifully next time - runs 25 mins or so and then dies.

Port engine battery not gettng any charge from the alternator and is just using up whatever it has stored to run the motor for 25 min ?

Starboard engine....no such issues.

Do you agree about the alternator? Is there a simple test to see if the alternator is working?

Appreciate your thoughts.



Big block Mercruiser
1997
Sea Ray aft cabin.

Alternator is not old at all, BUT it is FL and all mechanical gear takes a beating.
 
I agree with your assessment.

A quick check to verify is to measure the battery voltage before and after you start the engines and compare.
My guess is you will find the starboard battery voltage is above where it started and the port is at the same voltage or lower.

Do you have volt meters at the helm? What are they telling you?
 
Two other options if it ends up not being your alternator...

Last year my mechanic chased down electrical issues on my port engine. Engine would run fine then just shut off. I could restart by combining batteries. This isn't quite the same scenario you describe. For me it turned out to be the 90AMP fuse on the port starter.

This year, problems with the starboard engine. It would run fine for about 30 minutes and then just shut off. Almost as if I turned the key off. After it shut off I could crank it, but no start. After a few hours it would start and run fine... for 30 mins or so. According to my mechanic this turned out to be a faulty crank position sensor.

Maybe this helps
 
mrsrobinson said:
A trick I was taught many many years ago, with a car, was to disconnect the battery cables after it starts. If it continues to run, it's not the alternator. Not sure if this applies to a boat.
Click to expand...
That's not a very good "trick" at all for the same reason you should never turn your battery switch's of while the engine is running. It can and does ruin alternator's.
 
mrsrobinson said:
A trick I was taught many many years ago, with a car, was to disconnect the battery cables after it starts. If it continues to run, it's not the alternator. Not sure if this applies to a boat.
Click to expand...

And that will spark like crazy, not to mention can kill the alternator just by doing that alone. Just what you want in a gas powered boat ...

The easiest way to see if the alternator is bad is with the battery charger off for at least 30min. Start the engine and measure the voltage on the battery. It should be ~13.6 or higher.

I agree with your assessment @Rivertender , and you may also need a battery as well.
 
Deleted

That trick that my late dad taught me never destroyed a working alternator, nor did it ever cause anyone harm. Loosen the positive terminal bolt, start engine, remove/lift up the positive terminal, car continues to run, probably not the alternator. This was a poor mans way of testing what fancy gadgets do for you.

So, from my point of view, it was accurate. The OP can figure out if it's safe enough for him to try, or not, if he is comfortable doing it, or not. From his prior posts he seems like a smart guy. I took that into account before replying.
 
techmitch said:
That's not a very good "trick" at all for the same reason you should never turn your battery switch's of while the engine is running. It can and does ruin alternator's.
Click to expand...


I do have the Harbor Freight version of a battery tester. Will be using it tomorrow - battery has to be fully charged and then disconneted to rest for 30 mins, so I couldn't do it today.

Still looking for a quickie alternator test. Saw a good suggestion here. Shouldn't an ohm meter on the output contact on the alternator show something that is indicative if the alternator is even putting out?

Thanks to everyone here, I am feeling confident that it is the alternator, but, boy, that is a measure of work AND measurable money ---to be wrong - hah ha.
 
northshore said:
I agree with your assessment.

A quick check to verify is to measure the battery voltage before and after you start the engines and compare.
My guess is you will find the starboard battery voltage is above where it started and the port is at the same voltage or lower.

Do you have volt meters at the helm? What are they telling you?
Click to expand...


I will look at them tomorrow. Not sure. both I recall being beween 12 to 14 volts. I think the battery may be good despite its being 2021 becz it keeps charging up and stating the enginbe nicely.
 
To see if the alt is charging just test bat voltage before starting. Most likely it will be around the 12v range. Then see if it jumps to 13.6 - 14 volts after starting. You may have to bump up the rpms a little. If it is charging system related it is likely it is both charging sys and battery.The battery just got weak enough for you to notice. It can also be a module or pickup in the ignition that fails when warm. If you see >13v and it still quits it is likely ignition.
 
Rivertender said:
... Still looking for a quickie alternator test. Saw a good suggestion here. Shouldn't an ohm meter on the output contact on the alternator show something that is indicative if the alternator is even putting out?

Thanks to everyone here, I am feeling confident that it is the alternator, but, boy, that is a measure of work AND measurable money ---to be wrong - hah ha.
Click to expand...
SKybolt said:
The easiest way to see if the alternator is bad is with the battery charger off for at least 30min. Start the engine and measure the voltage on the battery. It should be ~13.6 or higher.

I agree with your assessment @Rivertender , and you may also need a battery as well.
Click to expand...
 
I don't want no sparks in my engine bay
 
mrsrobinson said:
Deleted

That trick that my late dad taught me never destroyed a working alternator, nor did it ever cause anyone harm. Loosen the positive terminal bolt, start engine, remove/lift up the positive terminal, car continues to run, probably not the alternator. This was a poor mans way of testing what fancy gadgets do for you.

So, from my point of view, it was accurate. The OP can figure out if it's safe enough for him to try, or not, if he is comfortable doing it, or not. From his prior posts he seems like a smart guy. I took that into account before replying.
Click to expand...
I've seen this done a bunch of cars without a problem but never on anything with a computer or electronic ignition.
 
Scott215 said:
I don't want no sparks in my engine bay
Click to expand...
Of course, nobody does, especially with a gasoline engine. As I've said many times here, this was for a car, and I never experienced sparks. And it was a trick, a tip, if you don't have the diagnostic tools with you, or own the diagnostic tools and want a quick test to try. That is what the poster asked for, so I tried to answer his question that way.

I am guessing none of the naysayers on this thread have ever accidentally touched a positive DC wire in your boat to metal, and it sparked? Or what about when using your volt meter to test something? Never ever never accidentally caused a spark? If you did, did it, blow up you boat? And again from previous threads and chats from the OP, I think he is smart enough to make this decision on his own, I simply offered a suggestion.

northshore said:
I've seen this done a bunch of cars without a problem but never on anything with a computer or electronic ignition.
Click to expand...
I did this about 6 months ago on my girlfriend's car. I did it as a quick test to confirm if it was the battery or alternator. The test worked, it was the battery, validated later with diagnostic tools.
 
I've seen batteries blow up before,so I disconnect the neg first
 
Scott215 said:
I've seen batteries blow up before,so I disconnect the neg first
Click to expand...
Greetings Scott,

The same amount of current that is flowing in on the POS term is flowing out on the NEG terminal - one can spark just as easily as the other.

Jump starting cars, 'they' always said make the neg connection to the frame or engine block and make that connection last. So if a spark did occur, it would not be right at the battery (where hydorgen density would be greatest)

I've also seen more that my fair share of batteries pop - I worked in the test lab for a company that built power wheel chairs (did a ton of battery testing) and also in the electrical engineering department of a company that made backup power supplies for CATV, telecom and traffic control boxes.

Sparks will happen if there is current flow and you disconnect either of the terminals.
In a car not that big deal as the hydrogen gas tends to dissipate due to the engine bay being somewhat open.
in a boat with (probably) less air moving around it is a bit more contained but being lighter than air hydrogen would tend to rise.

For me, I shut everything down that I possibly can and run the blowers for a bit before I disconnect.
Sulfuric acid is nasty stuff.
 
northshore said:
Greetings Scott,

The same amount of current that is flowing in on the POS term is flowing out on the NEG terminal - one can spark just as easily as the other.

Jump starting cars, 'they' always said make the neg connection to the frame or engine block and make that connection last. So if a spark did occur, it would not be right at the battery (where hydorgen density would be greatest)

I've also seen more that my fair share of batteries pop - I worked in the test lab for a company that built power wheel chairs (did a ton of battery testing) and also in the electrical engineering department of a company that made backup power supplies for CATV, telecom and traffic control boxes.

Sparks will happen if there is current flow and you disconnect either of the terminals.
In a car not that big deal as the hydrogen gas tends to dissipate due to the engine bay being somewhat open.
in a boat with (probably) less air moving around it is a bit more contained but being lighter than air hydrogen would tend to rise.

For me, I shut everything down that I possibly can and run the blowers.
Sulfuric acid is nasty stuff.
Click to expand...

To your point, with boats there are usually multiple batteries with there grounds all tied together. Removing the ground from one doesn't put the others out of service. And anything still powered could find another grounding path. The docks electric ground is also tied to the boat's ground so there is another factor.

I always turn the battery switch off for that battery and then pull the positive. That way nothing tied to that battery can find an alternate ground.
 
mrsrobinson said:
...

I am guessing none of the naysayers on this thread have ever accidentally touched a positive DC wire in your boat to metal, and it sparked? Or what about when using your volt meter to test something? Never ever never accidentally caused a spark? If you did, did it, blow up you boat? And again from previous threads and chats from the OP, I think he is smart enough to make this decision on his own, I simply offered a suggestion.

...
Click to expand...

If you have ever worked with live electricity be it AC or DC, you know to shut the breaker off in question before working with it, to avoid exactly that. And working with a voltmeter on a boat, is pretty tough to cross leads ...
 
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