Would love to know the final result on this one, as I have exactly the same problem. Idles on the drive without overheating. Put her under load and the temp shoots up. Bottom hose stays pretty cold, even when water starts boiling and glugging. Flushed the radiator (seemed to have good flow), tested thermostat, felt the waterpump impellers (didn't remove it), no loss of coolant (cap holds pressure)... yet she still wildly overheats now and then with lots of gargling coming from the "vent" pipe linking the head to the reservoir. Any wisdom anyone?