Corrosion - Mercury Outboard

[mgortel]

BOught a brand new Bass Boat last year with a 150 HP XR6 Mercury Outboard.<br /><br />Starting getting corrosion on motor.....actually corroding under paint making paint flake off. I noticed the anodes were not corroding at all. I removed them and noticed the motor was painted underneath the anodes so I scraped some of the paint off to get better contact between motor and anode. Anodes started working better (saw corrosion on anodes). <br /><br />Mechanic at shop said it looked like electrolysis.....however, I don't keep boat in water at same spot....etc. I did have a bad tilt motor and was wondering if the bad tilt motor may have been leaking current into motor which may have caused electrolysis <br /><br />OR<br /><br />if it was just the paint insulating the anode from the motor. I noticed there was still soem corrosion after scraping paint away but not as bad. Should I scrape rest of paint off between anode and motor.<br /><br />COuld the paint have been the problem? It looks to me like it was....however, why would Mercury paint the motor like that under the anodes if it would be a probelem?<br /><br />Any feedback or similar experiences would be appreciated!

 

[Fouled Plug]

Re: Corrosion - Mercury Outboard

Do you run in salt or brackish water often? As far as the paint, I've found that the screws holding the zinc on are sufficent to bond it to the motor. It does seem way early in that motor's life to start corroding away.

 

[62_Kiwi]

Re: Corrosion - Mercury Outboard

Hi Briggs - Has anyone checked the electrical conductivity between the anode and the engine body using a multimeter or similar ? This will show whether the anode is in place properly and getting a good connection.<br /><br />Fouled Plug is right that the motor is too new to show any corrosion at all. I have a 4 year old motor that shows none and has only ever operated in sea water.<br /><br />It sounds to me like a fault that was there in the motor from new and should therefore be covered under warranty - including any damage to paintwork caused by this fault. I'd follow that line before scratching paint etc.

 

[grandx]

Re: Corrosion - Mercury Outboard

Good idea to check for leaking current, it may have sped up the corrosion, but the fact that your anodes were not corroding and your engine was, is proof enough that your anodes were not making contact and not working properly. Now that you see them working, corrosion will slow down.

 

[DJ]

Re: Corrosion - Mercury Outboard

Riggs,<br /><br />I wasn't sure from your post if the boat remains in the water a great percentage of time.<br /><br />Couple things to think about.<br /><br />1. Does the boat have anti fouling paint? If so, is it copper based?<br /><br />2. Does the engine have a stainless prop.?<br /><br />3. Does the boat have "shore power" capability.<br /><br />If you do have shore power capabilty, that's where I would look for leaking current.<br /><br />The screws that hold the anode on should be sufficient contact. You would be better off to remove the anodes, rough them up a bit with sandpaper and reinstall.

 

[Kiwi]

Re: Corrosion - Mercury Outboard

djohns19 - what does a SS prop do in this instance ?

 

[DJ]

Re: Corrosion - Mercury Outboard

Kiwi,<br /><br />It would only be a factor if some of the other conditions exist, ie; copper based anti fouling paint.<br /><br />Disimilar metals can set up electrolysis. In this case, the aluminum usually loses.<br /><br />It may also be a factor if "stray" electric charges are lurking about from leaking "shore" current. Unfortunately, that is quite common in marinas.<br /><br />That's what the zinc's are for. Most people don't pay any attention to them until it's too late.<br /><br />In this case, hat's off to Riggs for keeping a sharp eye out.

 

[mgortel]

Re: Corrosion - Mercury Outboard

Thanks for the responses everyone!<br /><br />In response to some of the follow-up questions:<br /><br />1) I do not have anti-fouling paint on the boat.<br /><br />2)Boat does have a Stainless Steel Prop.<br /><br />3) I sometimes keep the boat at a pier for 2-3 days at a time. <br /><br />I have owned other boats that I kept in the same water for 6 months at a time with no corrosion. <br /><br />I did place a zinc anode in the water at the peir to check for any excessive corrosion that could result from stray current from electrical wires on the pier....BUT....the zinc anode has had absolutely no corrosion in 6 months.<br /><br />4) THe boat has a built in charger that is used to charge the trolling motor batteries. I never have charged it in the water though....I only plug it in to charge while it is on the trailer in my driveway.<br /><br />THe motor has a three year corrosion warranty, so I took it to a certified Mercury service shop to be looked at. <br /><br />Any other input would still be appreciated in order for me to have as much knowledge about possible. Hopefully they can figure out the problem.<br /><br />Thanks again for the responses!

 

[Gold Bear]

Re: Corrosion - Mercury Outboard

Riggs,<br /><br />Do NOT scrape the paint away underneath the anode. Doing so defeats the purpose of the anode. The sacrificial anode is suppose to do just that - be sacrificed. If you scrape away the paint - anywhere - then that bare metal will corrode. There is not supposed to be any electrical relationship between the lower unit and the anode, so scraping away the paint under the anode serves no usefull purpose. The anode is simply a metal that will conduct stray waterborne currents better that the lower unit - and be sacrificed in the process. In theory you could hang an anode over the side of you boat on a rope, and it would still do the same thing.<br /><br />Just my 2 cents, good luck.<br /><br />Gold Bear

 

[Fouled Plug]

Re: Corrosion - Mercury Outboard

Gold Bear, the opposite is true...the anode must be bonded to the protected parts. How can it conduct the current otherwise? On all of my motors, the zinc is held on by stainless screws directly through the metal of the lower unit. Even the "grouper" style overboard zincs come with a battery-type clamp on the end to secure to the metal of the hull/outdrive/motor. I'm sure a zinc on a rope would dissolve, but wouldn't protect the metals on the boat much.

 

[mgortel]

Re: Corrosion - Mercury Outboard

Fouled Plug,<br /><br />So it is possible that if there was some accelerated corrosion from some stray current.....that there was not enough surface contact between the anode and the motor since the motor under the anode was painted. The SS screws may not have been a large enough path for the anode to neutralize the stray current.<br /><br />THis would explain why I got much more corrosion of the anodes after scraping the paint off the motor where the anode contacted it.....increased surface area.<br /><br />WHat is the deal with the Grouper style Anodes....could they help if there was stray current in a marina or at a pier????

 

[DJ]

Re: Corrosion - Mercury Outboard

Riggs,<br /><br />That's exactly what they are for. They certainly can't hurt.

 

[singerjr]

Re: Corrosion - Mercury Outboard

djohns,<br /><br />You had mentioned about the electrolysis between the SS prop and the aluminum. I always had the understanding that SS was the best (most forgiving) to use wuth aluminum especially where strength is needed.<br /><br />Is this correct and that it is the lesser of evils or is there really no substitute and the electrolysis exists and is just as damaging as using steel (plated, painted or otherwise coated) What about brass and aluminum, just as bad?<br /><br />I work in the sign industry and we use a lot of aluminum and SS and there is sometimes this mystery problem when we think we have done it all correct. This could be the answer to the mystery.<br /><br />Also does water (rain - brackish - salt) further advance the electrolysis?<br /><br />Electrolysis has been an issue in my work but with SOME of my boating friends I can't bang my head against the wall enough to get them to believe it exists and causes finish and structural damage.<br /><br />Thanks

 

[62_Kiwi]

Re: Corrosion - Mercury Outboard

Riggs - don't scratch any more paint off your motor - exposing more surface area between the engine and anode is not the issue. Electrolysis is an electrical / chemical reaction - the flow of electrons, so the important thing is to have a good electrical connection between the zinc anode and the motor body.<br /><br />I found the following which explains it better and has some tips for diagnosing the problem;<br /> http://www.yandina.com/electrolysis.htm <br /><br /><br />Good luck with getting this solved !

 

[DJ]

Re: Corrosion - Mercury Outboard

Capt. U,<br /><br />Yep, it's the disimilar metal that causes the problem. SS props on aluminum outboards are fine, been around for years. Just make sure the zinc's are in good shape. Brass props caused more problems. Some outboard makers warned against using brass. They also warned against anti fouling paints with copper as a base.<br /><br />Salt, brackish and polluted water can speed up the reactions.<br /><br />This is usually NEVER an issue for trailerboaters. It becomes a problem when boats are left in the water. The "stray" electricity in some marinas is a real problem.<br /><br />Other things can add to this, as an example, poor grounds for electrical devices or not grounded to the battery(ies).<br />I think if I were Riggs, I would be checking electrical connections, etc.<br /><br />As far as your signs go, if the metal around a junction of disimilar metals is "charged" it will cause corossion problems.

 

[DJ]

Re: Corrosion - Mercury Outboard

Kiwi,<br /><br />Thanks a bunch for the web page. Great info.

 

[rlouns]

Re: Corrosion - Mercury Outboard

Wind - electrical storms (Lightning) causes the air to become charged and if there are any metal objects around they conduct the electricity whether you are at the waters edge or a field in the middle of no where.<br />Stainless Steel in my experience is a poor conducter of electrictiy and heat. (If you have an open barbecue use a stainless steel grate on it and you can pick it up with your bare hands on the outside edge even though the center is red hot). I had a machine shop make a mounting bracket for me to use on my CB antenna. The SWR's were so high I could not use it - poor ground - low conductivity. I wanted to eliminate the rusting of the brackets - didn't work.