First question. Where is all that water coming from? If there are leaks
then fix them. If it is condensation
then either ventilate the engine room / bilge or run a blower when you are running your engine.
For the steel components you have 3 options. You can ignore the problem, you can use a rust preventative or you can clean and paint / coat / plate. There are some good spray paints that can be applied to mechanically abraded steel surfaces. Plating is best done before installation
. Brush on zinc plate may also be effective.
For the alloy you only need to keep it clean and dry and the naturally occuring oxide will work fine.
There are a range of mild acidic treatment that can help but if you dont treat the components after rinsing and drying the problem will be exacerbated.
I'd start with a biodegradable citrus based degreaser and a stiff bristle plastic brush. If you use a wire brush use a stainless not a steel brush. The wires will lodge everywhere and rust like mad.
It will be lots of work to get that engine room looking good but well worth it. I dont tolerate any rust, dirt or moisture in either our engine room or bilge.
The comments re battery
outgassing are also worth taking note off. Sulphuric acid mist can create what you have.
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