you say theres pressure in the system all cooling systems run normally at a cirtain preassure it prevents the coolent boiling off to steam , having said this there could still be a problem sudgest changing the rad/expansiontank cap first as a corectl working cap will realese presure if it gets to much saving the engin from overpressure and giving a visual signe STEAM. i would sugest getting some one to test the system pressure as head repairs dont always take, please note there shuld always be antifreze in the system all year round
lee jcb mecanic
January 2011