MY10 3.0 TDV6 i have a problem with high coolant pressure. on short runs everything is fine. but on longer runs on the motorway at a higher constant speed the pressure builds up that much it blows the filler cap off the header tank and most of the coolant is blown out,
Had it to the main dealers for diagnosis they carried out various tests but could find nothing wrong, although they did replace the header tank cap.it made no difference. Is there anybody out there who has had the same problem and knows the cure.

Worked on a P38 RR with similar simptoms ended up being the water pump. Impels had broken up so the water wasn't circulating so overheated on anything but short runs.. 2008 G4 RRSport TDV8 current
2009 TDCi 90 current
2018 Discovery 5 HSE lux current
1994 Dakar current

Thanks for the reply Camelrock i will check the water pump out. i will let you know how it goes

Has anyone checked the radiator for partial blockage? That would produce the symptoms you describe. 2008 MY Java Black TDV8 HSE

Thanks Paddi will check it out

Thanks for the advice guys. sorry i have been a while getting back to you, i was getting nowhere so the garage i bought the car from agreed to take it back and run it for a few days to find the fault. it turns out it was the dreaded head gasket so body off and a week later and i got my car back.They completed the work under warranty. thank god ! and i took it out for a long run to the peak district last weekend towing our caravan with no problems at all so touch wood i hope that's the end of the problem.
once again thanks for your time and advice.