Found this black chippy stuff in coolant after analyzing everything from a bipolar running hot one day and running middle mark the next day issue.

blead system
no leaks
fans work
No debrees blocking radiator.

cools fine on highway.

 

that coolant looks pretty "milky"....possible bad head gasket or pin hole/crack in head

 

That pic taken under UV light? If not, that coolant indeed looks like the coffee I'm drinking right now.... :\

 

yes that’s a UV light so I can spot out the black specs. And I doubt it’s a serious issue. Car is well maintained. It’s something little I’m missing but you never know.

 

possibly the rubber seal around the radiator cap? Take a look at it and see if it's dried out.