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  1. #1

    Question 1978 85HP Evinrude overcharging

    Hi all. I have a '78 85hp Evinrude (85899c) that seems to be overcharging the battery. I have a volt meter in my boat and the last time I was on the water I noticed that it was reading 16 volts at any rpm above 2000. I changed the rectifier (it tested marginal) and it seemed to help but after running on plane for awhile the volt meter slowly creeped back up to about 16V. I doubled checked the guage and it is fine. So, I guess my questions are:
    1. IS this normal? Best I can recall is that my motor would charge to about 14V, not 16.
    2. Any suggestions on how to troubleshoot this. I can find information on troubleshooting a low or no charge condition but over charging seems to be nonexistant.

    I am a mechanic by trade and just got an Evinrude Service manual for this motor (but again it doesnt list over charging) so I am looking for any hints or past experiences that might save me some time and money.


  2. #2
    Join Date
    Apr 2010

    Default Re: 1978 85HP Evinrude overcharging

    This is normal on this type of system without a rect/reg on it. Make sure you have a battery with a large capacity and you may want to turn on your running lights when operating. BRP makes a regulator for this prob ( 173640 ) but it's costly. Awhile back there was a post on here for a cheap regulator. Maybe somebody will chime in with some more info.

  3. #3

    Default Re: 1978 85HP Evinrude overcharging

    Thanks for the info. Perhaps I'll look into the regulator. I use the big yellow wallyworld 27 series batteries so I think I'll be alright if I decide to leave it as is.

  4. #4
    Join Date
    Apr 2010

    Default Re: 1978 85HP Evinrude overcharging

    The 27 series batteries should be okay.

  5. #5
    Join Date
    Sep 2006
    Baton rouge, La, USA

    Default Re: 1978 85HP Evinrude overcharging

    Thats a known problem with evinrude/johnson motors of that vintage with rectifier only charging systems....if you put a new rectifier on it and see it at 16volts its only a matter of time before that rectifier will be shot.....your tac will also read funny..look normal at times (usually at startup) and then you will look down at it and it will read zero or be pegged etc....the fix is to put a regulator on the motor or use the recommended battery for the motor.....the bigger and better the battery the worse the problem will be.....a sealed or a gel battery is a nono...i dont have the recommended battery size for the motor handy nor the part number for the regulator....someone may jump in with them or you may search archives on the problem and find the info...in the meantime you need to increase your load with running lights or a 12v cooler or something....you still have the problem.....

  6. #6

    Default Re: 1978 85HP Evinrude overcharging

    Thanks for the information guys.

    I actually have the bigger 29 series batteries in my boat.

    The funny thing about my problem is that I have been running these big batteries for years (6+) and have never have an issue with the charging system reading over 14.5 volts. The only thing I can think of is that the last time I took the boat out, on the last day of the fishing trip we had a nasty storm come in on us and it was a rough boat ride back to camp. I have an old Starcraft supersport (more of a flatbottom vs a deep V ). We got back to shore and loaded the boat, broke camp and went home ( that was in june). In November we decided to hit the local lake and thats when I noticed the voltmeter reading 16V+.

    Because I never experienced an issue with the charging system prior to the "rough ride" in June and nothing was changed in the boat (batteries etc) I am beginning to think that maybe the battery was damaged during the ride and is causing my overcharge problem... I think I'll look into the battery and if it proves good, I'll go with the regulator.

    Does anyone have the instruction sheet available for the regulator so I can see what I might be getting myself into? Is it simply an add on device?

    Thanks again for you help.

  7. #7
    Join Date
    Apr 2010

    Default Re: 1978 85HP Evinrude overcharging

    If you buy a regulator the instruction sheet should come with it.

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