Have you had it checked out mechanically, or gone over it thoroughly yourself? When we got out 2006 X5 4.8is we had a 1,500 mile (just one way) trip coming up 2 weeks later. It ran great and appeared to be in great condition....checking the coolant it was down a little once but didn't really get my attention. I was still neurotic enough to pay the dealer to do Inspection I, and they found that the tank failed the pressure test. ...I was glad I was neurotic. We did the trip, 500 miles per day, and it was perfect. ...and for many thousands of miles of trips since.

I would probably get it looked over, but not everyone is as neurotic as I am. Have a great trip!