HAVE OVERHEATING PROBLEMS ON MY 2002 FORD TRANSIT JUMBO 2.4 DURATORQ (125PS)DONE 56,000 MILES

WAS OVERHEATING ONCE/TWICE A DAY LAST WEEK, NOW WATER SYSTEM HOSES PRESSURIZING AT IDLE SPEED, WATER BUBBLING IN WATER RESOVIOR. WATER PUMP WORKING OKAY, THERMOSTAT WAS REMOVED COMPLETELY TO TEST SYSTEM. RAN ENGINE WITH BELT ON (THUS NO WATER PUMP RUNNING) WATER SYSTEM STILL PRESSURIZING ! DOES THIS MEAN THAT IT IS PRESSURIZING BECAUSE GASES ARE GETTING INTO SYSTEM, HENCE CRACKED HEAD THEORY ?????

G HARPER, January 2009