I've been wondering about galvanic corrosion between two dis-similar metals. What is the factory fitting made out of? If it's magnesium or zinc, then the difference between it and the aluminum housing is small, and the fitting is the anode (the one that will corrode). Regular steel is the next least galvanic thing to aluminum, but that will make the housing the anode, so the fitting should be okay, but the housing will tend to sacrifice itself to the fitting instead of the other way around. Stainless steel (depending on the alloy) or brass are both further down the scale from regular steel, so would tend to accelerate the corrosion of the housing itself.
The good thing is the housing is quite large, so there are plenty of ions for it to shed before becoming a problem.
Anyone have a brass fitting in for a few years? How about steel? Has anyone noticed any deterioration of the crossover housing itself after dumping the factory fitting for a steel or brass one?
Of course, the better the coolant is maintained, the less electrolytic it should be, which may negate the problem entirely. I know that when I've seen old plumbing where galvanized steel pipe is fitted improperly to a brass fitting, it's the steel that gets the holes in it, which makes sense because the steel is the anode in that situation. That's with plain old culinary water. The galvanic charts I've seen are for sea water, and the fluid makes a difference in the potential, so maybe good coolant quality will negate the problem?
