Coolant change - Lower rad hose cold

[ontarioford]

I changed the coolant today and during each flush the coolant in the bottom of the rad would run cold for a minute and then hot water would begin to come out. The top of the rad is hot and the bottom of the rad is cold. Even after an hour trip home the condition remained. The gauge is mint and sits perfectly in the center. Half way, thinking I had an air lock, I stopped and removed the bottle cap, drove the rest of the way home and still the bottom hose is cold. Is the rad VERY efficient or is there an issue. It is currently -7C here.
Am I worrying about nothing or do I have an issue.
Many thanks

PS I did not remove the thermostat during the process I just flushes 3 times with DI.

Update: I installed a new thermostat this morning and the problem still exists.