Engine anodes advice please.

[Cathy*]

We have replaced our boat zinc anodes with aluminium but engine anodes are only available in zinc. We can have some aluminium ones made but not sure if it's necessary. The engines are inboard Steyr diesel. Each engine has 5 anodes and they are disappearing at a faster rate than the ones on our Nanni used to. Does it matter that we have the 2 different metals and are we better off keeping to zinc engine anodes regardless as the engines are almost all aluminium.

 

[superheat6k]

Aluminium anodes would provide zero benefit to aluminium parts as there would be no or at least little difference in nobility. Also most aluminium sold as stock for making things with is likely to be an alloy which may reduce its ability to work as an anode effectively.

Zinc is is less noble than aluminium so should provide protection assuming it is electrically bonded. But to be effective the zinc must be fairly pure, for instance it does not take much iron content to passivate the zinc.

You mention the zincs are working, but faster than on a previous boat. If you are getting 6 months I would be happy with that.

 

[Brent Swain]

A friend I built a 40 footer for, found rust in the built in keel cooler, so he added a bit of water soluable machine oil, which eliminated the problem, leaving the surface looking slightly oily.
I have been using it in my cooling system for several years now ,no problem.