That would be odd.

Here's the BMW training paper: page 45 shows it as #17 being part of the water cooling https://drive.google.com/file/d/0B1e...it?usp=sharing

As well as here you see it part of the water cooling system: RealOEM.com * BMW E70 X5 3.5d Cooling System Water Hoses

Not want to be a dick, but are you sure?