Under the link "How To's" ---> "X5 Tips & Tricks" --> scroll to Engine section, #7 "Lubrication 101"
http://www.xoutpost.com/articles/x5/...ion-101-a.html
It is very thorough and will probably explain why your oil is producing yellow gunk, and more importantly why you should drive at high temps at least once a week. (anyone with the yellow sludge issue would be doing themselves a huge favor by reading this great article-- posted by this sites Admin - big props and yet another reason to fork over a few bucks to join the site as a premier), I agree with one or two hot oil changes.
As for your coolant, you may have said already but it is imperative that you 1) use only BMW coolant (for its composition) 2) follow the distilled water mixture depending on climate (typically 50/50 mix unless tundra conditions), and 3)that the proper BMW coolant adding procedure was followed with burping the system, key on, heat on low, cap off- search for procedure....
hope that helps.