the first think 2 check is that it the system is blead corrcetly, beside the filler cap ther is a bleed screw open the screw it has a cross-slot head fill the rad until water flows cotinusly from this bleeder then put backin the screw set the internal rad to hot and let the engine heat

up then after letting it cool down open bleeder and top up water if it still heating up it time 2buy a gasket