Pathfinder coolant loss

Hi All,

Sorry for cross posting this, also in the Tech forums, didn't know which one would be better.

looking for help here on long-term coolant loss from Pathfinder 2.5 YD25ddTi engine 64k miles T-Spec.  System refilled and pressure tested by Nissan dealer, no fault found.  Recently called out RAC as car overheated, coolant in header tank (on min), no coolant in radiator.  Taken to different garage, refilled, pressure-tested to 3 bar for 15 mins, no leaks found.

Within 200 miles of this, heater only blew cold air.  Car stopped, 3 litres of water put into radiator.  No rough running or white smoke from exhaust.  Local garage now suggests taking the cylinder head off to check to see if the gasket is blowing.  Nissan main dealer says 'bring it in and we'll have a look', but seeing they didn't find anything last time, is it worth it?  Out of warranty. 

1.  Is a look at the cylinder head  reasonable?
2.  Why is there an airlock in the system so that there's coolant in the header tank and none in the radiator?
3.  Any other suggestions (I know US petrol Pathfinders from 05 have a history of trashing the automatic transmission because of radiator leaks, but I'm assuming that this has no bearing on UK manual diesel cars).
4.  Could it be something to do with the heater matrix?

The car's going in on Friday, if there are any good suggestions out there, I would like to pass them on to the mechanic.

regards

Ralph

Thanks Mick,

will let you know what they find,

regards

Ralph