Good point Mace
Do the pipes pressurise as the temp goes up. If the system doesn't hold pressure 1.1bar I think the standard cap is, then this will affect the efficiency of the cooling system.
But if the pump & thermo stat are good & all the hoses reconnected (in the right places) I'd be looking at an airlock. The 350z can be a right bugger to fill without getting an airlock.