Losing coolamt
3 Answers
Any coolant on floor while car is parked/stopped? You say that the car is loosing coolant, right? In any case, check coolant reservoir (bottle) could be cracked, also see if there is any sign of coolant inside the car, by the front of the passenger seat. The heater core is located behind the dash in that area and could be slowly leaking to the inside of the car.
I forgot the possibility of pin hole leak in the radiator. Take a close look at it like Tom says.