I have a 2008 Merc 115 opti that seems to suck voltage from the battery when it’s running, worse at higher rpms. The battery is a 6 month old odyssey 1500 agm (1050 MCA at 32) and is isolated from the boat’s electronics, including the bilge. The motor starts without hesitation and runs trouble-free at all rpms otherwise. All leads are tight and corrosion free. I do not set the battery switch to “both” when running.
This was a used motor, but a recent repower for me. It has about 250 hours on it.
I’m using the smartcraft gauges/voltmeter to watch the voltage drop. It will go from 12.7 to 10.9 (at which point the alarm sounds) in about 2.5 to 3 hours of running at over 3000 rpms. The previous owner reported no such problem, but his runs were short and he might not have noticed it.
There is no battery discharge when the motor is not running.
The motor is still under warranty, and one of the local merc “experts” replaced the alternator, which he told me contains the entire charging system. This did not fix the problem. He then did “everything he can think of” to find the issue, to no avail, including a teardown/clean/inspect of the vst which apparently sucks some voltage. He gave me the contact info for the regional Merc tech (?) to set up an appointment to have him look at it. (he apparently comes through every few months.) I have not done this yet, hoping to solve the problem sooner.
One other curiosity to me is that the alternator is reportedly putting out 24.5 volts at the alternator lead, as did the old one, and as “all of them do” on the opti’s according to this mechanic. I have not measured this myself, or taken measurments at the battery switch while running, but I would have expected 13.6v.
So, was this merc guy misguided? I have a service manual, but I would hope that the troubleshooting steps have been done by the mechanic already. Do I take it to someone else? Is there something I can check on my own with my digital electronic meter? Or, do I just break down and try to see this
carry the boat over to longshore marine, and ask to speak with Paul
I’m now at www.teamcharlestonmarine.com
Do what Chris said, exactly. Sounds like you may have been at another Merc shope…down the road? Telling you to call the Merc rep is piss poor customer service. I am pretty certain I know who it was, but you should post it.
I have the same motor. Please post results for future reference.
I contacted Paul as suggested. He’s already looked at the motor and it took him about 3 minutes to find the likely problem…the “fusible link” in the lead off the alternator is likely blown. This would essentially disconnect the alternator from the motor, forcing the battery to power the motor’s electrical stuff (fuel pumps, injectors, etc.) just like on a car with a bad alternator.
It seems this is not a very hard thing to check and diagnose if you know what you are looking for. With the motor off, he found 12V at the motor’s terminal where the battery lead is connected, but not at the alternator. The only thing on that lead between the two is the fusible link. If one did the same check with the motor on, you would see voltage at the alternator, and at the terminal, but might not realize that the terminal’s voltage represented the battery and not the alternator. I suspect this is what happened with the first mechanic.
This part needs to be ordered, but I’ll post back once it’s on to confirm that this solved the problem.
Thanks for pointing me in Paul’s direction! He’s been great to work with.
I had the same problem tested the fusible link and it was bad. A new one cured the problem.
Please tell us the “Authorized Dealer” that told you to call Mercury direct b/c he coudn’t figure it out, or didn’t want to spend the time. Everyone deserves to know so they can avoid the awful service your received.
thats why we told you to take it to paul
I’m now at www.teamcharlestonmarine.com
I don’t yet have the motor back, so I can’t for sure say the link is/was the problem, although it seems likely.
I’m not in the habit of badmouthing people on the net…I just think maybe the first guy was perhaps a little preoccupied with his Corvettes when he did the initial troubleshooting. 
cig
it never is a bad thing to take the high road
I’m now at www.teamcharlestonmarine.com
I hear ya. The corvette line definitely confirms my suspicion, which is all I was really looking for.
Feather,
Dare I ask how you knew?
He gave me the same line once…haven’t been back since. I was shocked at his “it’s not my problem” approach.
Longshore actually provides customer service!
Just pm me if you want all the details, I’ll be happy to tell ya’