2015 v40 d2 1.6 coolant issues
 

Hi i have a 2015 v40 d2 with what seems a common issue with the coolant pressurising ,i have changed the thermostat and housing , ive vacume filled it with new coolant ,ive driven it around with my diagnostic system watching the temperature live ,its all good for about 6 miles and then it loses heat from the blower and the engine temp hits 115 plus!! and its then pressurised. no smoke whatsoever out the exhaust ,oil is perfect ive done 2 headgasket tests and both came back negative ????