# Outboard Lower Unit Corrosion



## cutrunner (Jun 8, 2010)

So that white stuff is corrosion?


----------



## swaddict (Dec 19, 2009)

> So that white stuff is corrosion?


 I would assume, first time I have ever seen this happen. It's like a white powder that you have to almost scrape to remove


----------



## cutrunner (Jun 8, 2010)

You kinda got me there..
ive seen aluminum oxidize and form a thin white powder on top but yours looks excessive.
And why doesnt the last inch of skeg have any?

Was the boat sitting in he water for a couple days on your trip?
How do your zincs look?


----------



## swaddict (Dec 19, 2009)

> You kinda got me there..
> ive seen aluminum oxidize and form a thin white powder on top but yours looks excessive.
> And why doesnt the last inch of skeg have any?
> 
> ...


Boat was only in the water for a half day fishing trip, the part of the skeg that is not white was rinsed off with water.  The anode was replaced about 3 months ago.  The trolling motor is doing the same thing.


----------



## cutrunner (Jun 8, 2010)

Yea thats got me pretty puzzled.
if you have a volt meter, turn the motors battery switch on and put the black lead on the engines ground main ground that comes from the battery, and the positive lead to the lower unit. See if you have any stray voltage..
did you happen to tie up somewhere for lunch?, if so that dock can have stray voltage...
these are just guesses or somewhere to start


----------



## swaddict (Dec 19, 2009)

checked with volt meter and had no stray voltage to lower unit, checked anode under power trim n tilt, that looked ok.







  
Checked grounding wires and found this








Could this be the problem?  Was not tied up to a dock with any voltage


----------



## priscillatgorilla (Nov 29, 2014)

what you're seeing in aluminum oxide 

you need to check the trolling motor for "wet wiring" - this will allow a current to "leak" into the water,causing a stray current electrolysis...

that ground wire in the picture:

they're important - the motor needs to be fully grounded/connected electrically,for the zincs to do their job...

check the trolling motor - if you're unsure,take your boat to a qualified repair facility - they should have someone who's experienced with diagnosing a corrosion problem such as that.


----------



## priscillatgorilla (Nov 29, 2014)

> checked with volt meter and had no stray voltage to lower unit, checked anode under power trim n tilt, that looked ok.
> 
> 
> 
> ...



you would never have voltage to the lower unit - the "ground" straps are for continuity...


you need some specialized test equipment,to test for a stray current in the water from the boat

see my above post


you did notice how that zinc was at new,right ?? note the lack of wear ??
that ground strap,along with the strap near that zinc are a problem - you need to check the ground/continuity straps...


this will NOT cure the corrosion problem


----------



## priscillatgorilla (Nov 29, 2014)

> Yea thats got me pretty puzzled.
> if you have a volt meter, turn the motors battery switch on and put the black lead on the engines ground main ground that comes from the battery, and the positive lead to the lower unit. See if you have any stray voltage..
> did you happen to tie up somewhere for lunch?, if so that dock can have stray voltage...
> these are just guesses or somewhere to start



if that situation was occurring - the battery(s) would be dead,and the entire motor would be corroded away,also,odds are,the engine's "main fuse" would pop

it's possible,the 2 stroke yamahas have a few splices in the harness,down low -one could be wet,but odds are,something wouldn't work - tilt/trim - oil pump...

another point is where the battery cables enter the motor's cowling - possible....but again,it would cause a "drain" on battery,resulting in dead a dead battery...


a better way to test would be:

turn the battery switch on - turn everything in the boat off

disconnect the positive battery lead,to the switch,from the battery - use a simple test light.connect one lead of the test lite to the battery and touch the cable - if it lights,you've got a draw ...


----------



## cutrunner (Jun 8, 2010)

Any updates?
Have you used the boat since then and seen same or different results?


----------



## noeettica (Sep 23, 2007)

Badly Polluted Water


----------



## Creek Runner (Sep 1, 2011)

Your issue is caused from a stray current, meaning you have a break in insulation somewhere that is wet. The dead give away is the white powder and happening so fast. You can test this with a standard volt meter no special equipment needed. Back you boat in the water, hook your positive lead to the battery and dip you negative lead into the water. Now turn on your systems 1 at a time while watching the volt meter when it spikes then you found the circuit that is causing an issue. 

If the meter doesn't spike than reverse your leads, Negative to the battery and positive in the water, and repeat. 

It can be anything from your bilge, livewell, lights, trolling, to your main engine. 

Now stop using your boat, because if it is a stray current than it will corrode everything 100x faster. 

This could have also been caused by the marina you were staying at if they had a stray current from their docks or another boat had one next to you.

I have seen a brand new outdrives completely corrode to nubs in 3-4 days from a bad stray current in marinas


----------



## Creek Runner (Sep 1, 2011)

example, 

Maverick 2012 HPX18 started showing white powder on the lower unit and zinc anodes. (it will form 1st where the paint has been scratched) Corrosion began to form rapidly over 2 days. Performed the above test and found the live-well circuit was spiking, inspected and found that when the boat was rigged, they ran the positive and negative cables for the live well along the sea cock and tie wrapped them to it to hold into place. Well the wires were tie wrapped along the exposed threads of the brass sea cock, and the sharp edge finally cut into the wire insulation, and every time you turned on the live well not only were they exposed to the wet bilge but also salt water was running through the seacock where the stray current was. This happened at around 80 hrs and was fixed, 250 hrs later the boat had to be completely rewired because all the switches and connections were corroded to the point of major electrical issues. The boat was ran for about 4-6 total hours over a course of about 5 days and the effects of the stray current had already taken its toll on the electrical system. 

I discussed this in detail about 2 years ago on someone else thread on here, maybe Brett can find it for you and post a link. 

Creek


----------



## priscillatgorilla (Nov 29, 2014)

> Your issue is caused from a stray current, meaning you have a break in insulation somewhere that is wet. The dead give away is the white powder and happening so fast. You can test this with a standard volt meter no special equipment needed. Back you boat in the water, hook your positive lead to the battery and dip you negative lead into the water. Now turn on your systems 1 at a time while watching the volt meter when it spikes then you found the circuit that is causing an issue.
> 
> If the meter doesn't spike than reverse your leads, Negative to the battery and positive in the water, and repeat.
> 
> ...




close...but....


specialized test equipment is required to test this - it's called a silver chloride electrode.this is what's used to test for a stray current...


as I've typed above - it's probably a stray current situation,however - that zinc is clearly not bonded to the motor - it's in new condition - if that zinc was continuous with motor's ground - that zinc would've been gone....

aluminum oxide will form where the aluminum is bare,as in no coating....

as you're guessing,yes,i do have extensive experience/training in this area.


----------



## Creek Runner (Sep 1, 2011)

> > Your issue is caused from a stray current, meaning you have a break in insulation somewhere that is wet. The dead give away is the white powder and happening so fast. You can test this with a standard volt meter no special equipment needed. Back you boat in the water, hook your positive lead to the battery and dip you negative lead into the water. Now turn on your systems 1 at a time while watching the volt meter when it spikes then you found the circuit that is causing an issue.
> >
> > If the meter doesn't spike than reverse your leads, Negative to the battery and positive in the water, and repeat.
> >
> ...


That's not a grounding issue, and you can perform a simple stray current test with my procedure I posted above. You don't need expensive test equipment to do it in his situation, if you were trying to find a stray current at a marina were it could be underwater lines, multiple boats, shore cables or on a ship than yes specific test equipment should be used, but in this case it's not needed. Not my 1st merry go round either, been there done that got the shirt.


----------



## priscillatgorilla (Nov 29, 2014)

> > > Your issue is caused from a stray current, meaning you have a break in insulation somewhere that is wet. The dead give away is the white powder and happening so fast. You can test this with a standard volt meter no special equipment needed. Back you boat in the water, hook your positive lead to the battery and dip you negative lead into the water. Now turn on your systems 1 at a time while watching the volt meter when it spikes then you found the circuit that is causing an issue.
> > >
> > > If the meter doesn't spike than reverse your leads, Negative to the battery and positive in the water, and repeat.
> > >
> ...



it's very much a grounding problem - if that zinc is completely intact - it shows that zinc isn't electrically connected/grounded/bonded to the rest of the motor remember those continuity straps ??
if the zinc was continuous with the rest of the motor - it would be gone

you're in the right church,just a pew off...

the silver chloride electrode is used for measuring - it's needed...the inexperienced will also believe the testing can be performed with a copper strip and a DVOM

i'm guessing you have a seen a few old school merc bravo III drives corroded,yes ?? the outdrive comment ??

testing for stray current is performed the way I described - after the boat/motor have been wet for a few hours - not on trailer either - just the boat,floating...trailer will throw the testing way off...


I've been lurking on this site for a while -you seem to be pretty good for giving good solid info/diagnosis advice - guessing you're an advanced tech ??


----------



## swaddict (Dec 19, 2009)

update, did find the issue. the power wires for the trolling motor had rubbed thru the insulation and were pinched where the head meets the trolling motor shaft. replaced trolling motor wiring harness and all is good


----------



## priscillatgorilla (Nov 29, 2014)

> update, did find the issue.  the power wires for the trolling motor had rubbed thru the insulation and were pinched where the head meets the trolling motor shaft. replaced trolling motor wiring harness and all is good



nice !! glad to read you found the problem

next - perform continuity test on that zinc under the mount brackets - that zinc isn't "working"...


----------



## cutrunner (Jun 8, 2010)

Glad you found it
All 3 of us were right
Yes me and Creek are marine techs. Im cant say for him but i mainly specialize on outboard repairs, rarely do i have to deal with stray voltage and bonding issues, so if that is your direct field im all ears


----------



## priscillatgorilla (Nov 29, 2014)

> Glad you found it
> All 3 of us were right
> Yes me and Creek are marine techs. Im cant say for him but i mainly specialize on outboard repairs, rarely do i have to deal with stray voltage and bonding issues, so if that is your direct field im all ears



i'm a Yamaha/merc and Suzuki certified tech

I have just about 20yrs experience

part of general marine repair is corrosion diagnosis

you were taught about dissimilar metals immersed in seawater,right ?

like,not using a copper based paint on aluminum parts galvanic reaction 


you should've been taught/trained concerning zincs and continuity straps on outboards - controlling corrosion
that's a Yamaha/Suzuki and merc point of interest/discussion/training.

seeing a zinc completely "untouched" tells a lot to a "trained eye"


----------



## cutrunner (Jun 8, 2010)

Yes im fully aware of galvanic corrosion, dissimilar metals etc.
If you dont mind me asking, where are you located?


----------



## ranno (Apr 7, 2012)

Had a friend who kept his pool chlorine in the garage which caused excessive corrosion on everything.It started with a similar powder residual. Not say this is your problem but curious to know if you keep chlorine in the garage?


----------



## swaddict (Dec 19, 2009)

> Had a friend who kept his pool chlorine in the garage which caused excessive corrosion on everything.It started with a similar powder residual. Not say this is your problem but curious to know if you keep chlorine in the garage?


no chlorine in garage


----------



## swaddict (Dec 19, 2009)

> > update, did find the issue.  the power wires for the trolling motor had rubbed thru the insulation and were pinched where the head meets the trolling motor shaft. replaced trolling motor wiring harness and all is good
> 
> 
> 
> ...


that zinc does not touch the water (doesn't it have to be in the water to corrode?), I have a raised transom, I did clean the grounding cable o-ring connected to that zinc.


----------



## priscillatgorilla (Nov 29, 2014)

> > > update, did find the issue.  the power wires for the trolling motor had rubbed thru the insulation and were pinched where the head meets the trolling motor shaft. replaced trolling motor wiring harness and all is good
> >
> >
> >
> ...



notice where the bolts securing the zinc are - note the lack of aluminum oxide,on the bare aluminum areas ??

use a DVOM  set the meter on "continuity" - put one lead on the powerhead - a bolt - place the other lead on that zinc - it should have continuity - if not,there's a big problem and you need to find it...


yes,the zinc needs to be wet - to sacrifice itself - however,enough water will splash around to show a small amount of wear - with the stray current you had,that zinc would've showed wear.also,where the bolts holding that zinc in place,aluminum oxide would be present in those areas...did you perform a continuity test prior to cleaning that continuity a strap (ground cable) ?


----------

