I have an 04 Concode with a 3.5 litre engine with 96,000 miles. I just purchased the car and it looks like it has been sitting up for awhile. It runs great but overheats even though the guage shows it is withing acceptable range. There is no hot air coming from vents even after it overheat. I can tell it is overheating from steam coming from the engine and water boiling in the reservoir. What could cause these symptoms? Also, I do not have to add much water after it overheats

 

First likely air in the system due to the heater not blowing out any hot air. Low coolant no heat. Fill the tank up to the vary top. You can use a funnel to assist with burping out the air. Also on the front of the engine in the middle near the low part of the intake is a bleeder screw open it up let the air out and put coolant in the over flow tank