I also have a 2004, bought it in November of 2003.
This seems to be a common problem. It has happened to me 3 times. The first time I freaked out,

I was in upstate NY and had no choice but to drive it. My friend who is a mechanic was with me and looked at it and saw nothing out of the oridinary. No smoke and no signs of over heating. Needless to say after about an hour of driving the gauge went back to the normal reading. My oppinion is that it seems that the REAL cold weather plays havok on the computer, thus giving a false reading.
My Uncle has the same Car and had the same problem.
I dunno i guess it does not get cold in germany.

lol
We had a real cold winter here in the northeast, I dont see it happening durring the normal cold temps, (+10 or higher). Hope this helps.