#62066

Do some searches here on cooling. I think it has been covered well before. Just a few quick thoughts:

One thing about rads, sometimes an old rad just clogs up and cannot be cleared (esp if they have ever been left to dry out), even by flushing. You may have to get a reconditioned or new one.

Another possibility is that the lower hose is collapsing due to negative pressure; check there is a spring inside to prevent this.

Is it really getting hot or is your sender/gauge exaggerating the temperature?

Do you have a fan shroud (these help improve cooling)?

Has the coolant pump been fitted properly with a backing plate (where required)?

And yes, a new tight engine will get hotter until it is run in. I hope the piston clearances in the bore are not too tight if you had a rebore. If its just new rings it should not really get too hot.