[Hydratech®]

Electrolytic rust removal is wild, in that you can watch the rust melt right off, and also see how incredibly clean the coolant passages have become way deep inside of a cylinder head. What I am finding is that I appear to be up against the process in both parts of the actions - the electrical charge aspect and also the acidic actions. I thought I had an intake manifold (cast iron) figured out, by finish soaking it in a baking soda solution, thoroughly drying out in the hot sun (quite hot to the touch after an hour), then media blasting it afterwards to remove the initial flash rusting (that appeared while drying out in the scorching sun). As a test, we also then blasted another cast iron intake that didn't go through the electrolytic cleaning action.

The intake that was only blasted has successfully stayed on the shelf here in the climate controlled shop without any noticeable corrosion forming in 7 days time already - just removed from the blasting cabinet and thoroughly blown clean. The intake that we put through electrolysis, quenching in a baking soda solution for 48 hours, then dried hot to the touch out in the sun, then blasted clean barely made it 24 hours sitting next to the other intake before starting to flash rust again (doh).

So either there is still some acidic activity still deep in the pores of the cast iron (my best guess right now) that doesn't want to neutralize in the baking soda solution (that is supposed to do it), or the electrical charge process is still affecting the casting lighting off flash rusting. Despite the hellacious heat and humidity outside here in TN right now, indoor shop readings are 72 degrees and 40% humidity. Removing the part out of the solution and drying off as quickly as possible with two air hoses wide open on the part indoors does nothing different, versus using a single blow gun outside in the fiery sun. As the part dries, here comes the flash rusting. A quick dip / spray down with Evaporust seems to help, but then becomes blotchy with dark mottled spots of Magnetite forming, with flash rusting still forming in places. I will have to try the Kleen Strip Concrete and Metal prep - might just do the trick, especially if you say you pressure wash the parts first. Do you dry the part before applying?

Since this has been happening, I am going to try some smaller cast iron test parts to see what may happen if I:

1) Oven bake the part to say 250 degrees after removing from the baking soda neutralizing solution. Maybe this will cook the parts into not flash rusting further by outgassing anything still hiding under the surface.

2) Will try the DIY plating angle as a finishing step, as it seems to mirror the electrolytic cleaning steps BUT using a sacrificial anode in a last step in a separate tub. Maybe this will feed the cast iron a barrier that can conclusively seal it. If this works, it may be even cooler still by not only quelling the flash rust, but also lightly plating the casting for a possibly improved appearance. Not sure yet, thinking to try zinc or copper. A greyish colored casting with zinc maybe, and a copperish colored casting with copper? Anything other than flash rust will be a win.

3) Spraying or dipping the casting down in straight antifreeze as soon as it is pulled out of the neutralizing solution. We have all seen cast iron water pumps and thermostat housings that are rusted to all hell on the outside, but immaculate on the inside, running a mix of water (which would induce corrosion) and the antifreeze inhibiting the corrosion. I have been thinking about it but haven't tried it yet. Could it be that simple? Likely no, but worth a shot.

I also understand that many castings are phosphate dipped during initial manufacture to seal any porosity and inhibit corrosion. Just blasting the surface of the casting may be what is not disturbing the overall metallurgy, while the ultra-deep cleaning electro-chemical reactions are going much deeper into the castings. While driving any corrosion out hiding under the surface of a casting seems to be providing a stunningly clean part, watching it change right before your eyes into something less is disheartening. I am determined to find a solution (no pun intended) for the problem. If / when I do, I will let you know. On the flip side, if somebody has anything further to offer that I can try, I am all ears!