A leak.
Since a vehicle's cooling system is closed and sealed, antifreeze (coolant) loss will occur due to leaks which can be in any part of the system, such as the radiator, water pump, heater core, transmission cooler, hoses, or a blown head gasket.
Blown head gasket or cracked head.
Can be leaking intake manifold gaskets, which can sometimes be fixed by using Dexcool coolant. Can also be a head gasket.
A LOCA is a loss of coolant accident. A rupture in the main coolant system resulting in a major leak of that coolant is a loss of coolant accident, or LOCA.
From air trapped in he block of your engine. If you recently drained your coolant air is trapped in the system. You will need to bleed all air from the cooling system. If you have not recently changed the coolant this is a sign of a blown head gasket. Other symptoms are white smoke from the exhaust, loss of coolant with no apparent leak, oil level overfull, and a white foamy substance under the oil fill cap. Stop driving the vehicle unit this is repaired.
hello, have you changed the spark plugs in this vehicle?
many possible causes, low coolant, worn out coolant, bad thermostat, no circulation (water pump) radiator blockage, pressure loss somewhere
some general causes: leak in cooling system (including possible blown head gasket) resulting in loss of coolant; defective thermostat
Look on the ground! Monitor the coolant reservoir.
Normally a leak in the sytem, either internal or external. More details would be required to expand on the answers to be given
A cracked head could also at fault.
Heater core leaks, depending on severity, may present with several symptoms which include fogging on inside ofwindshield with coolant residue (smears instead of evaporates when wiped), coolant or antifreeze smell in vehicle and otherwise unexplained loss of coolant from radiator reservoir.