Be absolutely sure you took the engine heat way past the boiling point- that is 100 degrees C. or better
When I rebuilt my engine several years ago I was overly concerned at not letting the new engine get too hot. I even went so far as getting a custom radiator made ( copper with 3 rows ) and it made little difference . It wasn't till I let the engine cycle thru several 120 degress or more several times was I able to burrp all the trapped air out - it is the trapped air somewhere in the cooling system that impedes water flow,that gave me grieve.
Now with the larger rad , engine temp is around 87 to 90 ( highway ) ambient temp. 25 C. The big rad now seems a waste of money.
When filling the rad with coolant to the top, replace the cap, then fill the coolant bottle with the hose attached to the rad and held higher that the rad and fill it to the correct mark- gravity will fill the rad and over flow hose and bottom of coolant bottle - you are trying to expel as much air as you can before you even start the engine.
This is documented in the manual. I read it but didn't follow it to the letter .
The overflow outlet is on the filler neck , on the back side of the rad and runs over the top of the engine and down to the bottom of the overflow bottle. It is a closed system.
good luck
" If you can't say what you think, very soon you won't be able to think !
OKANAGAN FALLS. BC ,Canada