Water pump or thermostat?
 

Hey I have a 2002 audi A4 Quattro. I just replaced the reservoir after it had a small crack on the bottom. Now I have to keep putting some coolant in. My car isn't overheating and the temperature doesn't ever really change. I'm not sure if I should get the radiator flushed, or replace the thermostat, or the water pump... I'm lost.