2000 Dodge Neon

I have 95,000 miles, 4cyl, 2.0 L. The car was overheating so I added 50/50 engine coolant. I used half of the container. 5 days later, it started to overheat again so I added the other half. Now 5 days later, which is now, it started to overheat again. The engine fan comes on, there does not appear to by any leak. I added it to the overflow tank. Should I be adding the coolant directly to the radiator? Could there be anything else be wrong?
February 15, 2007.

The coolant has to be going somewhere. You should fill the radiator when the engine is cold, and fill the reservior to the proper level.

Then run it, at idle and wait for the temperature to come up and see what is happening.

The thermostat may be stuck, is your heat real hot?

May be more serious problems such as head gasket if it is burning it. Is the exhaust white or a rough idle present?

I am in Florida so its difficult to tell about the heat. There is nothing white in the exhaust and it is not having a rough idle.

I am going to fill the radiator and see what happens

Feb 15, 2007.
I'm inclined to think the thermostat is stuck at this point.