go to youtube and ask that question...easy..
um i think you miss spelled the title lol Radiation :P sucked a couple rads in the car huh hehe. any ways draining the entire system needs to be flushed and you will have to do it with water. if you don't have compressed air or the proper tools to refill the system it may be more advisable to just have a garage do it Preferably one that specializes in audis and vw's. Most dealers also will offer a particular deal to do the work as well but could be more expensive then a specialist shop. Here is a video of a guy doing the same job and another in between. https://www.youtube.com/watch?v=FJf2X6ENnP4
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