First thing to do is check your coolant level. If it is low and there is no obvious sign of a coolant leak, fill it back up and then turn on the vehicle with the radiator cap off and a funnel that has been fit to the diameter of the radiator neck.
Turn on the heater to max and run the vehicle until the air coming out of the vents is very hot. Most of the air pockets should have been expelled by this time. Turn off the vehicle and reinstall the radiator cap and top off the coolant level within the coolant reservoir. Then let the vehicle run and reach operating temperature (probably about five to ten minutes). Check for leaks around the coolant hoses, radiator, heater hoses at the firewall etc. The coolant hoses should be somewhat firm to the touch (be careful it may be scalding), and the coolant is under pressure. If there is a leak anywhere it should be more apparent when the cooling system is under pressure. If there are no leaks--periodically check the coolant level to see if there is any loss and wait and see....
shef, December 2009
