One more thing, electrolysis occurs through the coolant and will pick the most reactive metal and use it as a sacrificial anode. This is usually aluminium but not all aluminum is the same. They are alloyed differently depending on the casting process used and the temperatures and forces it will experience in service. The water inlet on Isuzu Gemini engines used to be super sensitive to this because of the type of alloy used.

The best protection is a top quality coolant / glycol. Mobil, penrite, valvoline, shell, make sure it is O.E. quality. I used to visit ACL gaskets when they were in business, and they would to test glycols for there affects. Some of them used to accelerate electrolysis!!!!