How many shaft anodes?

[mjk1040]

I think Viper may have miss spoke on which type to use where. I believe I was told zinc for salt water, magnesium for brackish water and aluminum for fresh water. I tried to get aluminum engine anodes and was told they were not cost effective and thus not offered and to use magnesium. Check all your engine anodes too. I believe those people at boatzincs know their stuff!

[PossiblyPaul]

Very interesting discussion above. Replacing all of my zinc anodes this month (finally) I went with the leading provider (so I'm told) in the UK, who advised aluminium for all of them, and I've added a couple of rope-cutter combinations to the shafts.
I'm in a small coastal marina, mainly sailboats but with a number of motorboats, and a fishing harbour close by. I have a suspicion that the screws holding the trim-tab plates were - very quickly - eroded more by electrical effects than anything else, and the resultant holes in the hull damn near sunk the boat last year; a very close watch on that this year!

[Viper]

QR_BBPOST....mag for fresh water and aluminum for salt and brackish....

QR_BBPOST I think Viper may have miss spoke on which type to use where. I believe I was told zinc for salt water, magnesium for brackish water and aluminum for fresh water......

Nope, I got it right! Aluminum anodes are for salt and brackish water, magnesium anodes are for fresh water only. The growing trend is to move away from zinc for salt water. And as I explained above when considering the metals involved in the application's running gear, aluminum can be used on fresh water inboards too as it'll be more active than the shafts, rudders, and props. Because sterndrives and outboards use aluminum casings, I prefer magnesium anodes for those although the alloys in aluminum anodes are still more active than the alloys used in the sterndrive and outboard casings.

[V12diablo]

Is there anodes on the Mercruiser 7.4 MPI engines, if so where would I look?

Jason

[Viper]

Not normally unless it's closed cooled and the type of heat exchanger you have has one.

[V12diablo]

It is closed loop, I’ll check the heat exchanger out.

Jason

[Viper]

Go to the link below and enter your serial number. It will give you a parts breakdown. If you don't have the serial number, go through the directories on the left until you narrow down your model. The serial number is the best way though to be sure.
https://www.mercurymarine.com/en/us/par ... ts-catalog