Rainer,

The only thing I can think of is that your missing either the belly pan, or the air dam. These two thinks keep debris from flying up an messing the bottom of your car up as well as helping it cool. These are two plastic pieces located directly under the engine, and directly under the radiator below the air intake. What is your coolant guage showing are you full. I have a 96 960 sedan which is basically the same exact car that you have except for yours is a wagon and mine is not. I have my car on a track at least once a week at 120+ mph and have never reached above midpoint on my temp guage. When my air dam did fall off I noticed that the car would run a little hotter.

Brandon