There are quite a few different things that can make your Audi overheat, so I will not even try to list them here for you. I will do you one better, though! I am actually a published (and paid) author of a great article that tells you how to diagnose an overheating engine. It is a simple process that will walk you through a few steps that will pinpoint the problem, without even using any tools. It has helped millions of people, and I am certain that it will help you, because I wrote it for people like you. So here is the link to:Diagnosing an overheating engine
Anyways, if that helps you, then you can even follow me on Twitter, for more great tips and tricks that will help you save a ton of money on car repairs. that one is twitter.com/acoates23234
Thanks for asking, and good luck!