On Sat, 21 May 2011 09:25:01 -0400, Jay wrote:

On 5/21/2011 7:17 AM, tem wrote:
I have 1986 Mercruiser 170 (mdl MCM 170) w/ 2 battery system. This may
be a dumb question, I'm not a mechanic. My volt meter reads 12.3 on each
battery when engine is not running and 12.2 after I started it. Does
this mean my charging system is not working? Any help or advice is
appreciated.




Could be. Check it with another voltmeter to be sure.

Yes, good advice. Digital voltmeters are very inexpensive these days.

The batteries should read somewhere around 12.6 volts with the engine
not running. When the engine is running, normal voltage is in the
range of 13.8 to 14.4 volts. If it turns out that the alternator is
defective make sure that you replace it with a marine spark protected
unit.