Take the cap off, run the car with the heat on full blast til heat is cranking out the vents. Rev the rpm's to 2500 or so for a few seconds at a time. Add coolant to reservoir. Mine took a couple times of doing it on different days til I got all the air out, but I lost a good bit of coolant when replacing the thermostat. If you are sitting at idle and the heat gets cooler from vents, add more antifreeze to reservoir.