Late to the game, but wanted to toss out some comments about those Cathar made regarding 304/316 stainless. We use these materials frequently for items with variable water contact, ranging from stagnant to turbulent and varying between submerged or not. Generally speaking, in my experience rust is only a problem if the steel has been contaminated, generally by manufacturing processes that handle both stainless and plain carbon steels. A good passivation process normally takes care of such contamination.
That said some of the water we deal with does have bad actors that will attack the 18-8 family of stainless. In many of these cases this is addressed through either going to a duplex stainless ala 2205 or a specific paint procedure.
I would not expect the fluid contents and temperatures of a typical water cooling system to cause any trouble for 304/316.
I'm just wondering what experience or data has led to your conclusion regarding the rusting of 304 and 316.
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