Hey, I'm pretty sure of the answer already, but I just wanted to confirm it before I put out any money. I have been loosing coolant, which now just stopped happening. My car has developed a light burning smell after normal driving. When I looked at my expansion tank, it had almost a white powdery crust on it. At first I thought it was my after-run pump, but this leads me to believe it is the tank itself. Does this sound right? It's a b5 s4 with approx 118xxx miles. Thanks!

 

Yup, time for a new tank.

 

This happened to me a few weeks ago i was just pissing it out all the time. But it just recently stopped as well. when I took it in they looked and saw that there was a hose that was leaking. They said they would have to of pulled the top of the motor to get to it and it wouldnt be worth it to do it, after taking it in and having them look at it tho it has stopped leaking for some reason. no coolant. lol jk