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Old 19-05-2020, 14:49   #1
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Outboard with battery charging question

Hello, apologies if this is a stupid question:

My 9.9 Mercury outboard is having some trouble pumping water so I disconnected it from the battery, took it off, and brought it home. I want to run it from home but I read the following line in the manual, "IMPORTANT: Outboards with battery charging capabilities must not be operated with battery cables disconnected from the battery. Damage to the charging system may result." Is this only a warning to make sure you take the charging cable off, or am I going to damage the outboard if I manual start it at home?

Thanks!
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Old 19-05-2020, 15:35   #2
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Re: Outboard with battery charging question

Don’t start it without a battery hooked up. At least borrow your car battery a moment for testing.
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Old 19-05-2020, 15:36   #3
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Re: Outboard with battery charging question

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Originally Posted by Chotu View Post
Donít start it without a battery hooked up. At least borrow your car battery a moment for testing.
Sounds good. Thanks!
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Old 19-05-2020, 16:34   #4
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Re: Outboard with battery charging question

When is the last time you replaced the impeller?
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Old 19-05-2020, 18:00   #5
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Re: Outboard with battery charging question

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Originally Posted by thomm225 View Post
When is the last time you replaced the impeller?
I am a new owner but I believe the impeller was replaced sometime in the last two years. I detached the lower unit and checked the impeller, it looked OK to me. Boat is used in salt water, so my guess is the previous owner wasn't flushing as often as he should've and there is some sediment buildup. I saw a video where somebody uses a drill to rotate their driveshaft to test if the lower unit is pumping water, that's probably my next task
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Old 20-05-2020, 06:10   #6
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Re: Outboard with battery charging question

Quote:
Originally Posted by Clived View Post
I am a new owner but I believe the impeller was replaced sometime in the last two years. I detached the lower unit and checked the impeller, it looked OK to me. Boat is used in salt water, so my guess is the previous owner wasn't flushing as often as he should've and there is some sediment buildup. I saw a video where somebody uses a drill to rotate their driveshaft to test if the lower unit is pumping water, that's probably my next task
Did you remove and inspect the impeller?

I had one fail and it looked fine, but after I removed it I noticed that the rubber portion had become disconnected from the center/hub portion.

The hub turned but the rubber impeller did not as the shaft spun.

Also if you ever have the lower unit off and the impeller is a year or so old, you should replace it.

And lastly, my outboard is 9 years old and is used all the time in salt water. I think I may have flushed it 12 times in that time.

I do run it though at least once every week or two even in Winter.

It's a 5 hp 4 stroke Mercury Outboard (2011)
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Old 20-05-2020, 09:06   #7
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Re: Outboard with battery charging question

I had an 8 HP outboard with a generator for ten years. You learn something new everyday. I had no idea.
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Old 20-05-2020, 09:16   #8
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Re: Outboard with battery charging question

Quote:
Originally Posted by Clived View Post
I am a new owner but I believe the impeller was replaced sometime in the last two years. I detached the lower unit and checked the impeller, it looked OK to me. Boat is used in salt water, so my guess is the previous owner wasn't flushing as often as he should've and there is some sediment buildup. I saw a video where somebody uses a drill to rotate their driveshaft to test if the lower unit is pumping water, that's probably my next task
Salt build up in the water exit tube or passage in the case is very common. Not sure about that engine but often you can push a copper wire or similar through the rubber water exit hose under the cover, (~ 1/4" hose) or up through the exit hole in the case etc to clear the blockage. Literally every time I've thought I had a bad impeller it was salt build up instead.
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Old 20-05-2020, 10:00   #9
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Re: Outboard with battery charging question

Quote:
Salt build up in the water exit tube or passage in the case is very common. Not sure about that engine but often you can push a copper wire or similar through the rubber water exit hose under the cover, (~ 1/4" hose) or up through the exit hole in the case etc to clear the blockage. Literally every time I've thought I had a bad impeller it was salt build up instead.

X2 Have a business that runs outboard boats and have yet to replace an impeller for failure. Always have the "piss stream" clog up. You should fresh water flush it also. A lot of engines do this without starting the motor. But if it's got a battery charger then yes hook up any 12V battery to it before running.
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Old 20-05-2020, 15:41   #10
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Re: Outboard with battery charging question

To give a background on your original query - always have a battery connected to an alternator when you run it. The rectifying diodes will get damaged if not.
Re the impeller and water passages, others have said it all, but as a general rule, if salt water dries in the cooling passages,yes salt will build up. If passages are hot then that salt cakes on and will need mechanical or chemical cleaning. It has to be severe to block passageways but if certainly does happen. Always try to flush with fresh water after use
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Old 20-05-2020, 16:12   #11
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Re: Outboard with battery charging question

My 5hp Honda has a 12v outlet for charging a battery in case you have an onboard GPS or depth sounder etc.
There is no requirement to have anything attached on the Honda.
I presume it's a bit like the 8A 12V outlet on most cheap gennys?
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Old 20-05-2020, 16:13   #12
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Re: Outboard with battery charging question

I knew you shouldn't disconnect the battery from a motor with an alternator, but is this the same as having no battery connected to a small motor having just a charging coil in the flywheel?

Not sure I have accurately described the charging device on a small outboard, but whatever it is, I have run my electric start 30hp Tohatsu with no battery connected (pull started, obviously), but later and with a battery, it charged just fine.

So I figured there is a difference. No?
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Old 20-05-2020, 18:45   #13
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Re: Outboard with battery charging question

Quote:
Originally Posted by thomm225 View Post
Did you remove and inspect the impeller?

I had one fail and it looked fine, but after I removed it I noticed that the rubber portion had become disconnected from the center/hub portion.

The hub turned but the rubber impeller did not as the shaft spun.

Also if you ever have the lower unit off and the impeller is a year or so old, you should replace it.

And lastly, my outboard is 9 years old and is used all the time in salt water. I think I may have flushed it 12 times in that time.

I do run it though at least once every week or two even in Winter.

It's a 5 hp 4 stroke Mercury Outboard (2011)


And thatís the key. If your unable to fresh water flush the outboard then run it at least once a week. It keeps the salt from crystallizing in the cooling passages......least thatís what I was told by an outboard mechanic years ago and it has worked for me.
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Old 05-06-2020, 14:53   #14
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Re: Outboard with battery charging question

Sorry to be tardy - I had opened this a month ago but it got lost in a sea of tabs...

One thing to know about Mercury outboards, at least older ones, is that there were two options available: a lighting kit and a battery charging kit. IIUC both include an additional (to the magneto) coil that mounts inside the flywheel on the top of the block, which would of course produce something like 12V AC. The lighting kit has a regulator that outputs regulated 12VAC for incandescent lighting, and if there is nothing attached it is fine with that. The battery charging option rectifies and regulates the output to 12V DC for charging purposes, and requires a battery to be attached in order to run without damage. Apparently you have the latter so never run the engine without a battery. I have the lighting kit which I used with incandescent nav lights, but have since bought battery-powered LED nav lights and no longer connect to the 12V output.

These engines are not designed to survive long in salt water. The assembly screws are installed dry at the factory and they readily become corroded in place such that full disassembly is not possible. The right thing would be to use something like Tef-Gel when assembling.

If not getting cooling water out then always check that the tube from the water pump to the block is in place in both grommets (at each end) - an easy mistake to make. If there is really enough mineral buildup to block the cooling flow then the right thing to do is to break it down completely and remove all of the scale. Once there is build-up in the engine pieces can break off and lodge in the exhaust stream so just clearing the exhaust flow is only a temporary fix.

Greg

Edit: What was the cause of the cooling problem?
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