I worked in a shop for years, and was a service manager after that (not BMW). When a customer came in and told us what the problem was, we ignored it. We listened to what the symptoms were. Nobody knows what it should sound like as much as the owner does. But if owners knew what the problem was, they wouldn't need trained mechanics. Sorry if that sounds arrogant, but customers doing self-diagnosis are actually pretty funny most of the time.

Describe the symptoms to the.dealer. What is the pitch of the noise, high or low? Does it vary with engine speed or road speed? Forward or reverse? Engine hot or cold? Specific rev ranges? Is the noise the problem, or a symptom of another problem? What else happens when it makes the noise? You get the idea.

If you are paying for the repair, ask for an investigation and quotation, don't sign a blank cheque work order. But let them do their investigation, and expect to pay for that diagnosis.

By the way, coolant doesn't make noise, so why would coolant be the problem? And there is no such thing as an engine thermometer. Thermostat, yes. And temperature sensors. But no thermometer.

Good luck.

__________________
2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue