OK, ClubSeaRay......Let hear your advice

CaptBobO

CaptBobO

Member
Aug 31, 2020
49
Boat Info
2000 410 Sundancer
Engines
8.1L Mercruiser Horizon
I have a 2000 410 Sundancer. New to me.
Lately, I have been dealing with immediate drop in voltage and engine shutting down at idle speed. At initial start up, I have 14.2 volts. I can cruise around for 30 min at around 1000 RPMs with no issue.
Then, while docking my engines immediately just shut down and voltage drops to 12.4 and I cant restart the boat. I have to plug in to shore power and wait till the batteries charge back up and then it will start just fine.

Here is what I have done so far:
All new batteries
brand new serpentine belt (thought it was slipping)

The only thing I have done so far to the boat, was install a new stereo head unit. No new amps or anything. all stock still.

I just bought a new alternator for the port motor because I thought that could be the issue, but after putting on a new belt, my volts jumped up to 14.2 so now I am thinking its not that.

What the heck is immediately draining my batteries at idle speed?
I may try running my genset next time I'm idling to keep everything charged, but that doesn't seem right to have to do that.

Anyone else fight this gremlin before?

Engines are 8.1 Horizon
 
Must be something that both engines share together, since they both have separate batteries and charging systems. 12.4 should be enough to start them, strange.
 
Do both motors die at the same time? Electronic ignition and ecm need a minimum voltage to run. I would install that new alternator as a starting point and see what happens. Do have a separate battery to start the generator? Is so start it and run the charger off the generator to get going again.
 
I don't think it's th cause, but I would double check th main grounds on both blocks. On the 454's there is 7 terminals under one bolt and caused me issues.
 
hottoddie said:
Do both motors die at the same time? Electronic ignition and ecm need a minimum voltage to run. I would install that new alternator as a starting point and see what happens. Do have a separate battery to start the generator? Is so start it and run the charger off the generator to get going again.
Click to expand...
Typically, the port motor goes first, then the starboard right after.
I cant start either until it charges back up. I watch my voltage on my Garmin display. its steady at 14.2 while idling around 1000 RPMs.
when docking, and it dies, I look at the voltage on the Garmin display, and sure enough.....its 12.3.
Ill change out the alternator today.

My gen has a brand new separate battery.

The part that gets me though, is WHY does it effect the starboard motor as well?
Are they somehow tied together?
 
I had an issue when I ran my starboard battery down and wouldn't start. Started the port and when I was tried to used the emergency parallel button, when I tried the starboard, it would kill my port.... wondering if you have something shorting that switch out or the 2 banks out....it's a stretch. But it's really strange that they both go out at almost the same time...
 
Sounds normal that it would show battery voltage after the stall but why don't they start with the 12.3?
How high does the voltage need to be for a restart? Does this every time? What if your only running 1 engine?
 
Assuming it has an battery isolator, if that has failed, it could become one bank.....
 
Chris-380 said:
Assuming it has an battery isolator, if that has failed, it will become one bank.....
Click to expand...
How can I tell if the battery isolator is shot? any test I can run for that?
Also, is the isolater installed on the bulkhead in the engine bay behind the black cover?
 
Check your voltage at the batteries while charging with engines. Confirm they too are at or near 14v during normal operation.
 
Ok, new alternator is installed.

13.4 volts with engines off
14.5 with engines running at idle

Going to let it idle with shore power off, and all accessories on and see how long it lasts till shut down.
Praying it doesn't get there and just keeps burning fuel
;)
 
Sound so like the isolator is junk. It is pulling the amps to he dead side and causing both batteries to become weak. You then charge them back up and all is good, until you take it out of the slip again.
 
Also Che k the alternator breaker if you are just getting your voltage reading from the alternator and not back at the batteries.
 
mquiet said:
Sound so like the isolator is junk. It is pulling the amps to he dead side and causing both batteries to become weak. You then charge them back up and all is good, until you take it out of the slip again.
Click to expand...
Can anyone tell me where the battery isolator is located at?
2000 410 Sundancer
 
I don't know exactly, as I have a 480 sedan. Mine is located just forward of the batteries. It is a rectangular bar. I would follow the battery cables and they should lead to it.
 
Remember that battery voltage might read 12.3 but when you put a load on it you might not have enough to start. As said before, if isolator fails and it combines both batteries, you might be running on 1 battery and the bad batteries bring down the good batteries
 
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