2002 Volkswagen Jetta Hello I have a question

My car is overheating everytime, but when I come to a stop it cools off to normal. After a few seconds of driving it starts overheating on me. It has coolant and all. Yesterday I put a new thermostat on it along with a plastic fitting that was cracked and today I replaced the thermostat censor and it still over heats. My brother is a great mechanic but couldn't figure out how to get the air out of the radiator! Do you know of a way beside keep burping it when it starts to heat up? I could use some help and thanks in advanced. Contact me with your I added a picture of the cracked piece we found but it was on the other side of the motor from where the thermostat was. Once I did this I will make a big a$$ donation