I am guessing this is electrolysis but whenever i remove my radiator cap there is pressure in the system. I have never this before on my other miata.
It is a koyo 55 running either straight water, or water and a little water wetter. My car does not run hot even in 100 days.
Do i get one of those caps with the sacrificial metal? I always worry it going bounce up and down dent the tops of the cooling tubes.
Or I could do nothing.