Heat Exchanger rust

[johnneale]

Its fitted to a BMC 1.5 captain and I got a problem.
The heat exchanger body is cast iron, whilst the inner tube box is a mixture of brass and copper. The end covers are also cast iron and are rusted internally around the mild steel (I think) securing bolts.
The heat exchanger is not bolted to the engine and is electrically isolated
I have rebuilt the rusted out casting with plastic padding and replaced the bolts with stainless.
Have i fixed it ?? or should I connect it electrically to earth ???

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[brianhumber]

You have a mixture of metals with conducting electrolite fluids as is the case with all metallic heat exchangers forming a Galvonic cell. Unless you have something like zinc anodes fitted in the end caps the next most vunerable metal in your heat exchanger according to the galvonic table will act as the anode and disappear.
Options - fit small zinc anodes like the sea water cooled Volvos have in their cast iron blocks or replace HE as a ppm measure every few years. All depends on how long you use the vessels engine ie the time HE is in use for every year. I replaced my Bowman body after 14 years and 3,500hours as an example.

Brian

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