I had a similar experience. After changing the radiator the top hose connection blew off a week later. I might have made a mistake in reconnecting it but why did it last a week? Long short cut short, I changed the radiator cap for a new OEM one from a dealer and the problem (which included the coolant level dropping by an inch and I now suspect was the cause of the old rad' blowing) and have had no problems since. The cap was not releasing pressure and it was making it's way out elsewhere. My local non franchised specialist has had similar issues with after market coolant caps and will only fit OEM ones in a Land Rover box.
