Pressure Cap rating: Thanks Jack! The car came with 20 psi on svivel, done by the previous "smart" owner; I think he applied it because the overflow tank was "dead"/rotted away. I UNFORTUNATLY continued with this mistake. NOW I GOT 12 psi! As cooling system is top notch think this pressure is good enough, I have a 13 psi as spare as well.
Overflow tank mods: Ok I see plastic container is also an issue, however the idea with a sight gauge has something to me. Got the difficulties of it as well now. On all my cars (6) as all older models, I open the hood look at the water tank and know in a second I am good or need to add, I am seeking for something like that. .
TX team for all your thoughts and insight... and pacients !
Matthias