Gauge on helm reads 12 volts, 13 when revving engine?

[edsmax]

Normally my "volt" gauge on my helm reads around 14v when cruising. Tonight when I started her up at the dock, gauge read appox 12v. Put drive in nuetral and revved engine and would not get past 13v.

Next step check alternator output at the batteries? If so, test at both batteries? I have two. I have never had to diagnose this kind of issue before.

On a side note, I unplugged shore power while engine was idling and engine ran fine. I wanted to see if engine would stall, lights dim, etc...but all seemed normal. This was done at night with all cabin lights on, deck lights on, blower fan on, etc.

Ed

 

[Lazy Daze]

Start by removing and cleaning your battery cables. Follow the cables and remove/clean/protect every connection you come across. See if that makes a difference. Also, take a look (best you can) at the cable ends where the jacket starts - look for corrosion that has wicked it's way up there. This cleaning may or may not solve your problem, but it's a good first step since w/o clean connections, everything else you check may be skewed. Besides, it's a good idea to do this every so often as PM.

 

[Steve Craig]

Had the same issue with my Sundeck. Just bought it used. Gauge showing 12.0-12.5V with RPM at about 3000. This should be close to 14.0.
First step I took the batteries out & had them load tested. It's normally a free test at any automotive/marine battery supplier.
One was dropping down to less than 9V under load, the other just under 10. I bought two new batteries right there.
I didn't get a chance to get a voltmeter across the old batteries while charging but the condition made the decision for me.
Batteries will get to a point where they won't accept a charge no matter how hard you try.
Mine were mis-matched- 800CCA & 650CCa, both different manufacturers.

 

[Theresamarie11]

Question(s): was the shore power on so the batteries were fully charged? Did you just run for a couple of minutes?
For your thread, sounds like you have both house and start batteries, and do you know if you have a auto charge relay or is there a switch or are they in parallel? Usually a 2 battery, single engine boat will have a switch or relay. I had a charge relay one on one of my boats and it charged my starting battery first, and then my house battery. On my boat the house battery was shown on the guage, not the starting battery. If the battery is low (whichever one is guaged) it could take a bit of time to come up to the 14V and it will not happen instantly (if it was down a bit). Let it run a bit to see if it comes up (and make sure it doesn't go down), check your water levels (use distilled water), voltage at battery, connections, etc as others have said. Also, make sure your charger is working (shore power breaker didn't trip).

 

[edsmax]

ISSUE SOLVED - My serpentine belt was incorrectly routed by a mechanic when they changed my seawater pump a couple of weeks ago. The engine would run, but it had way too much play at the longest point between pulleys. I removed the belt and reinstalled it the correct route per my mercruiser manual. After tightening it up, I started the engine and the gauge was back to 14V. To be sure, I tested the alternator output at both batteries and it tested fine. Im glad that I checked the belt routing first - took me less than 15 minutes to fix this issue.

Ed

 

[Lazy Daze]

Good deal! Don't count on all your fixes being so easy, though! :smt001