[abhik]

If you are driving the car out on a hot summer day and in traffic then 1/2 on the temp guage is fine as the same happens to me because the air around the car is hotter in traffic due to the heat from other vehicles in close viscinity thus the air sucked in is also hot resulting in the higher temperature but it should fall down a bit once on an open stretch. So i guess nothing to worry about but anything more than that then do get the coolant changed or check for leaks, sometimes it might not be a visible leak and the coolant might be trickling away slowly somewhere unnoticed.