Mate, usually a blown head gasket is caused by over heating of the engine which in your case might have caused by a fault in your engine cooling system (radiator, cooling fan mulfunction). Neo6 is a very solid engine and built to handle any sort of beating thrown at it so clearly u r long distance driving couldn't have caused u the mentioned problem... however it could have escalated the problem which would have been there since the day u bought the car from the dealarship. If the car has done over 100,000 Ks u could expect this sort of a radiator problem because in Japan one owner does not own the same car for more than 3-4 years (abt 50,000 Ks) and more Ks on the clock more negelected it is on the maintainance side. I'm a private importer and have imported many NISSANs over the years.
