With the vehicle warmed up and running feel both heater hoses with your hands. If one is hot and the other is luke warm or cold, the heater core needs to be flushed by itself. Flushing the whole system doesn't unclog the heater core. Disconnect both heater hoses from the engine, fabricate a fitting to attach a garden hose to one of the hoses. Direct the other hose into a container and gently turn on the water until the water runs clear, then reverse hoses and run again until clear. Reattach hoses to engine and refill reservoir.
could be the water pump That is a typical symptom of an air lock in the cooling system
The electric cooling fan or cooling fan temp sensor may be faulty.
The thermostat tries to control the heating and cooling in you home to maintain a comfortable or energy efficient temperature.
There is an engine temperature sensor that operates the cooling fan.
Purg The Air Out of the Cooling system
Water pump defective.
are the cooling fans coming on
Thermostat stuck open or heater core clogged. Bad radiator cap or small hole in cooling system.
Have your cooling system serviced. Drain, flush, and coolant replaced. Install a new thermostat.
sounds like the heater core is out or you have an air bubble in the cooling system
Any sign of overheating, just replace the thermostat. On a 8 year old car it should be replaced and the cooling system serviced.
you might want to check for a blown head gasket or a cracked head or block. espically if it loosing water out of the radiator with out leaking on the ground.