Yvan;

It sounds to me like you just need to REALLY fill the cooling system...it overheated because the rad is only half full...and the syphon effect to refill from the overflow bottle doesn't work when the rad is that low...

Here's the technique that I use to fill the sealed system: Fill the rad, start the engine (rad cap off), and wait until the thermostat opens (indicated by level dropping), and refill the rad right to the top, open the flow to the heater core by turning the heat to hot...top up rad again if required...only then, seal rad with its cap, and fill overflow bottle half way. Try that and let us know what your temp does...

Cheers