Hybrid turbo will flow more air at the same boost level, so if I presume you're on standard management it's probably running lean and then getting hot.

Also, isn't a Fiesta rad smaller? Could be something that simple.

The valve you mention, do you mean the thermostat? If so, chuck that into a saucepan and heat it up. If it opens just before the water is boiling it's fine and you should put it back.