I also have a 2003 Alti and have the same problem. What I have learned from other forums is this; If your radiator cap is over 2 years old, buy a replacement before stating this procedure. Lift the front end of the car on ramps or something. Any way you do it, the front end must be up. Of course, take all necessary safety percautions. Open up the radiator by removing the cap. Turn on the car and turn on the fan to the highest speed - in the heat setting. This will supposedly purge air pockets in the lines. Fill the radiator all the way up to the very top. Keep an eye on it for the level may drop (thermostat opening?) if so, keep filling all the way to the rim. When satisfied the level is no longer dropping, put the NEW cap on BEFORE shutting off the car or you may give the radiator a chance to "inhale" thus causing air in the lines again. Lower the vehicle, fill the resevoir up to the "full" mark (I'd personally fill it even higher) and cross your fingers. Hope this helps someone.