Coolant Leak

if its a small leak (long time between refilling) it could still be a heater core because the air flow will carry and dry the coolant usually leaving a stain the same color of the coolant at the foot vents and a sweet smell when first used. but thats getting ahead of ourselves. coolant goes low because of leaks either into the car, onto the ground, burned off the engine (stains and smell again), or into the combustion chamber from a bad head gasket (may make white exh smoke or misfire on starting). use your eyes and nose in and outside the car, and a pressure tester to check for leaks.