I have a 1997 A6 2.8l quattro sedan. It has about 171k miles on it. Today, after getting my tires replaced I drove around somewhat aggressively, but never redlined. The temp gauge never went past normal, but when I parked it and left it for a few minutes it was dumping boiling antifreeze. At first I thought my car was smoking too, but all the smoke was coming from the antifreeze I was parked on a slant so it all ran into a puddle. I opened the hood, nothing was steaming and aside from the overflow tank nothing had any fluid on it. It ran for about an hour before it was shut off. Earlier this morning I drove it an hour and a half into the city to get the tires replaced. Could they have cracked the overflow? I still have enough coolant to drive, but I'm cautious about it until I can look at everything. Would I just need to replace the overflow tank and the tubing?

 

I'd replace the coolant "overflow" tank. I had a small crack in the one on my 5000 a couple of years ago that was shooting a fine stream of coolant straight into the back of the radiator. I thought the radiator itself was leaking and got a new one.. Turned out the stupid tank was the issue. It's really not just an overflow tank like the older cars. This tank is pressurized with the rest of the coolant system so if a small crack forms, it will shoot out under pressure and drain in short order.