||the radiator as far as it will go, leave the radiator cap off, turn the heater in the car on full HOT and heater fan speed on high, and run the engine up to full operating temperature.
Usually when the interior air is very hot, the coolant has circulated in the complete cooling system. I add coolant as needed when the engine is running.
I then turn the car off and put the radiator cap back on. Over the next few times when I drive it, water may get sucked from the over-flow tank after I turn the car off and it cools down if more coolant is needed in the radiator.
I check the level in the over-flow tank to keep it at the specified level. This approach has always worked for my 94TT.