so the low-mounted reservior ("white bottle" by the radiator) is for READING PURPOSES only, and the high-mounted reservior (silver metal/aluminum container by the intake manifold) is for ADDING PURPOSES?...but if the engine keeps drawing from the lower-mounted reservior, then wouldn't the high-mounted reservior always be full until the white bottle's coolant is gone, but then it'll be too late because "However, if your expansion bottle ever runs completely dry, it will allow air into the system, and could allow the coolant in the sealed part of the system to expand enough under lack of pressure, to boil and overheat"...
Could you explain a little more cuz this noob's GT consumes about a cup of 50/50 coolant every month or so (5EAT with lots of traffic driving), thanks!