Outdrive corrosion

[Misty Blue]

Let's pick your brains.

My wifes boat, Deb's Joy, is a 1968 century with a 160 Mercruiser. Yea, it's cool. The outdrive is a rebuild and I do not know it's history. I use magnesium annodes for cathodic protection but the outdrive still shows signs of corrosion.

There are loose white powder-like crusts here and there that I assume are aluminium oxide. Also the paint is coming off in places. I can see bare metal.

Any suggestions on how to stop this from happening? Sandblast, prime and paint? What products? Take it to a body shop? Gregorian chants?

Any thoughts would be welcome.

Misty Blue.

[Paugus Bay Resident]

Unfortunately, you're not alone :( This might give you some ideas (http://www.finishing.com/204/15.shtml)
There are some really good epoxy paints on the market. The main issue is that the outdrive housing is aluminum and really needs to be etched before painting.

This months Powerboat Magazine had an article on it as well.

Gregorian chants can't hurt :D

[Dave R]

Here's what I did:

I sandblasted the whole drive to remove the loose paint and corrosion and to rough up the existing finish where it was still in good shape.

I carefully sandblasted the spots where the anodes attach so thet they were completey bare.

I carefully taped off the areas that should not be painted, like the boat, the decals, the SS bolts, the hydraulic rams etc.

I primed the whole drive with zinc chromate primer and then shot it with Mercruiser phantom black paint.

I installed magnesium anodes and my Bravo 3 drive has been fine ever since.

The whole process took me about 8 hours and it was pretty easy. The sandblasting was easily the most miserable part

If your magnesium anodes are not making a good connection to the drive, they won't help at all. Try to clean the aluminum under them until it's completely bare and re-install.

Oh and cool boat BTW...

[Woodsy]

Misty...

All of the more modern boats have an electrolysis system on them. On the Merc it is called MerCathode. Its an easy retrofit and I don't think it costs too much. I would seriously consider installing it after you buff & fluff your outdrive as Dave R suggested.

Woodsy

[gtxrider]

I am not familiar with the shifters on the OLD Mercrusier out drives but we had a friend with an outboard that used electric shifting. There was a coil in the lower unit that had a short to the case and it chewed up the rivits on the transom of his aluminum boat. Just a thought, I still get them every now and again.

Mercrusier 160? That means it is running an OLD 250 Cubic Inch Chevy 6 cylinder that first came out in 1962 as a 194 Cubic Inch engine in the Chevy II...Talk about a work horse engine. The same basic design is used in the current 4 cylinder used for the 3.0 Liter only with 2 more cylinders.

P.S. The 4 cylinder has been used for years as a Midget Racer engine.

[Dave R]

Misty...

All of the more modern boats have an electrolysis system on them. On the Merc it is called MerCathode. Its an easy retrofit and I don't think it costs too much. I would seriously consider installing it after you buff & fluff your outdrive as Dave R suggested.

Woodsy

True. The mercathode "kit" could be bought for just over $100.

I'm thinking that maybe some of the continuity cables, assuming it had them, are broken or missing.

[Misty Blue]

'Sounds like a chore but Dave Rs plan is the best. I'll do some research on Mercathode as well. I have heard of it but thought that it was unnecessary on the Lake.

And yea Woodsie, they put the tachometer in the boat to remind you that there is an engine runnning back there!

Again thanks. Misty Blue.

[Dave R]

'Sounds like a chore but Dave Rs plan is the best. I'll do some research on Mercathode as well. I have heard of it but thought that it was unnecessary on the Lake.

And yea Woodsie, they put the tachometer in the boat to remind you that there is an engine runnning back there!

Again thanks. Misty Blue.

One more thought, do you have an SS prop on the drive? SS is far more noble than aluminum so the prop will essentially make your outdrive its sacrificial anode if the other less noble (zinc or magnesium) anodes are not working properly. Mercathode was introduced solely because the drives it came with had no other options except for SS props. You have to be vigilant about good connections to the anodes with an SS prop. Mercathode will surely help.

One issue with mercathode though, it needs to be active any time the boat is in the water and that takes battery power. If the boat is left unused for a long time, mercathode will drain the battery. If you install a battery charger on the boat and attach it to shore power to keep up with the drain, it's possible to dramatically worsen the outdrive corrosion. Shore power can do this through stray currents from floating grounds that allow some current to flow through the sterndrive and the water. This can be prevented with a galvanic isolator. All of this costs money.