Hi,
the video gives you a step by step tutorial how to replace the thermostat valve on a Passat 35i with the 2l 2E engine. This valve controls the water flux to and from the radiator. In addition the thermo switch for the fans at the radiator is replaced. Both parts have the tendency to work less and less correct with the time. If your Passat has problems with the engine temperature, i.e. it's too warm in the summer or it's too cold in the winter time, this is the first repair you should do.
http://www.youtube.com/watch?v=bGwXvW-fNjY
The video has a German sound track, but English subtitles are available at YouTube. If you don't see them by default, watch the video directly on YouTube and press the subtitle button below the frame.
Enjoy it,
Jürgen