Vauxhall cavalier sri 1992 ,2litrs, 8vavles?

i have replace the gasket cylinder, piston rings on my cavalier sri, it boils up before reaching 90 degrees celcius.when i replace another radiator switch of 45 degrees celcius, the fan works and it does not boil up.please help to avoid the boiling up and that it works at 90 degrees.thank you