Coolant level

Check the coolant level in the coolant reservoir. Make sure it is between the "F" mark and "L" mark.

Fig 1: Identifying F And L Marking On Coolant Reservoir
Courtesy of KIA MOTORS AMERICA, INC.
If the coolant level in the coolant reservoir is at or below the "L" mark, add coolant to bring it between the "L" and "F" marks, then inspect the cooling system for leaks.