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.

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.

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.

On May 21, 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.

--
tem

Did you take a direct reading off of the Alternator while engine is
running? Thats where I'd start.

On May 21, 8:54*am, "*e#c" wrote:
On May 21, 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.

--
tem

Did you take a direct reading off of the Alternator while engine is
running? Thats where I'd start.

One thing to check, as you have dual batteries, what position is/was
the Battery Select Switch (I would assume there is one) on while you
were doing voltage checks? Depending on who wired everything
originally, well....who knows! You should have about 14.3-14.7 VDC
when the emgine is running above idle and with majow loads turned off.
12 volt batteries are generally concidered to be 100% charged @ 12.7,
3/4 @ 12.25, 1/2 @ 12.2, and so on (readings taken 24 hrs after any
charge/discharge action) I'd check at the Alternator, then at batt #1
(with the batt select switch at Batt1. bhen at batt #2 with the batt
select sw at batt2, then at either and both with the select sw at
"all".
Good luck!
Mike

On May 21, 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.

--
tem

There are a number of ways that could be wired but generally that
doesn't appear to be enough voltage to be charging.

Your basic 2 battery switch connects the system to one or the other or
both of the batteries. That includes both the alternator as well as
the rest of the rest of the 12v system. More advanced 2 battery
systems may have separate charging circuit that connect the alternator
to both batteries independently of the battery switch. They are a lot
less common than the basic setup.

You could try the system with the switch set on each battery alone and
check the voltages running and off. If you have the switch in the
both position a single bad battery could be causing misleading
readings. Right after starting the motor you should see around 13.8
volts.

The original charging system on these motors is a real nightmare. If
it is broken and has not been converted to a regular alternator you
might want to consider doing that. The initial investment is a few
hundred unless you are competent to fabricate your own brackets. But
after that you can use ordinary one wire marine alterators which you
can get all day for under a $100.

On May 21, 6:17*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.

--
tem

If I remember correctly the 170's (also 470's) had a low amp stator
mounted behind the harmonic balancer, that would eventually give out
and cause a lot of grief. I've seen somebody on evil-bay offe3r a
conversion 'kit' which consisted of a marin-ized , internally
regulated 10-SI delco alternator and the appropriately made brackets
to hang the alternator on the engine and run via a belt, but they're
pricy, like in the $3-400.00 range. But then again, this would provide
much better reliability, 65 amps (+/-) of power and easy service if
necessary.

You might wish to check out this thread as well:

http://www.marineengine.com/boat-for...harging-system