this is my worry , regarding pressure testing of the system, when i first noticed it after that as mentioned above i took isb to khi trip , kept one coolant bottle with me in car for the safe side but did not notice any reduction in level, then i went to my job abroad, my wife was driving the car in city, daily traveling was hardly more than two to three kilometers, when i came back, checked the level found reserve bottle was empty.
i was in gilgit hunza trip where first time i noticed reduction in level, level was reducing when i was driving car on 4x4, i also had doubt on cyl head gasket , i started car for long time without radiator cap did not find any bubble in the coolant, which normally indicates head gasket leakage, not sure if toyota coolant water evaporates, or other thing could be, not starting radiator's fan on time, which is quite rare