Outboard Sacrificial Anodes

[springsDS2]

I just purchased a 1983 Evinrude Yachtwin 4 hp outboard. I want to minimize corrosion, and I noticed that you can get an anode kit for the motor. Just wondering what the group's experience has been with corrosion and sacrificial anodes, and what is in this kit. Also I would like to replace some rusted bolts. Zinc coated steel bolts are corrosion resistant, but since the anodes are made of zinc, will these bolts corrode more quickly.

[GreenLake]

If you have zinc coated metal bolts together with parts that are plain steel, for example, the zinc on the bolts will act as the sacrificial anode.

Adding more zinc will protect them partially, in that some of the anode function will now be taken up by the proper anode. However, unlike the case of dissimilar metals (e.g. zinc anode and propeller in a different metal), the zinc in the anode cannot protect the zinc coating on any screws.

The whole point of the anodes is to provide a metal that gets corroded first (the zinc) which prevents the steel from corroding. It does so by setting up a voltage differential between the zinc and other metals.

Adding corrosion protection should be a no-brainer if you are using the motor in salt water. The anodes work only while they are submerged, by the way, so rinsing your motor when you take it out of the water remains a good idea.

[springsDS2]

That's great info. The motor will be used in salt water, and I will rinse it after each use. So I should put zinc anodes on the motor, and use plain steel bolts, yes?

[K.C. Walker]

Gregg,

I have a 70s Johnson version of that 4 hp motor. I think it's a great choice. It's nice and light with low vibration and pretty quiet. I'm amazed at how often mine starts on the 1st pull. The other thing about these motors is that parts are readily available and they are easy to work on.

I don't know what bolts you're talking about but I'd stick with stainless wherever you could. If you're talking about the lower unit, I'd especially stick with the stainless. Even a small amount of rust in that location is going to screw you up. It's always a good idea to use zinc anti-seize paste when you set these bolts.

As GreenLake pointed out, the anode will only help you out while the motor is submerged. In my case that's a very small amount of time in saltwater. I always rinse down when I get home which includes flushing the cooling system. That's pretty quick with one of those earmuffs style things you wrap around the intake and connect to the garden hose. I don't use an anode.

KC

[springsDS2]

don't know what bolts you're talking about but I'd stick with stainless wherever you could. If you're talking about the lower unit, I'd especially stick with the stainless. Even a small amount of rust in that location is going to screw you up. It's always a good idea to use zinc anti-seize paste when you set these bolts. KC

KC, I know this is only a problem when the motor is in the water, but what about the galvanic action between stainless and aluminum. They are far apart on the galvanic chart which is not ideal. I had found in the past with an outboard my family had, that stainless bolts caused severe corrosion around the bolts. So much so, that they were nearly impossible to remove, and caused the aluminum to deteriorate in that area.

The bolts I'm thinking about are the ones that attach the gearcase to the midsection and other exposed bolts that have rusted heads.

Gregg

[K.C. Walker]

I'd go to a marina/boatyard that worked on Johnson/Evinrude and by the original equipment bolts. I think you will find they are stainless. You do need to seal them up with either anti-seize or something like blue Loctite. If the bolts are sealed no salt water gets in so no galvanic corrosion. Then all you have to worry about is the bolt head not corroding, I think stainless works best in this situation.

However, I would go by what the shop guys at the boatyard recommend. These guys deal with it all the time and I don't.

KC

[GreenLake]

You can use Tef-Gel around the bolts if you are worried about seizing or corrosion. (Unless, that is, if the Tef-Gel makes it so the bolts come undone too easily. ). Tef-Gel is also used with any SS fasteners that you put into an aluminum mast.

[springsDS2]

You can use Tef-Gel .......

Thanks for the tip. I have ordered some zinc anti-seize, so I'm going to use that for now.