2010 2.4 puma overheating issues

Hi guys new to the landrover scene here total novice and I've recently purchased one a 2010 110 utility 2.4 puma and I've had nothing but problems from day 1 the issue started with slight loss of power a few seconds after it would be fine and all power would be restored after a few times of this happening the temp gauge would all rise with the loss of power and its building quite alot of pressure that much pressure it actually split the header tank/coolant expansion tankin two halfs and put quite a large dent in my bonnet but only happens on occasions some time it can last 50 100 miles no problems no smoke at any time hot or cold so I've taking it to my local LR specialists and they had it on diagnostics with no fault codes at all the did a gas test on the header tank and said ether the cylinder head is gone or the water cooled egr valve has any would on here had any similar problems and managed to solve them I've replaced the radiator and header tank water pump seems OK aswell tia any help is appreciated and welcome

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