First things first, if you're losing that amount, then you've either got:-
Loose coolant hose/s
Split hose/s
Hole/s in rad or split/s in end tank/s
Split/s in header tank
Badly leaking water pump
Badly leaking w/p gasket
Badly leaking stat gasket
HG/s failure
Internal fracture/s to engine block's coolant gallery/s
I'd try to address this issue first and get it sorted. Then you can address the running/sensors issue later. No pointg in doing it the other way round!
Last edited by joz8968; 16 January 2011 at 04:58 PM.