Check your expansion tank as well. Excessive coolant on the drive belts could have resulted in the alternator slipping, reducing electrical system voltage resulting in what just might turn out to be a temporary transmission issue.

2002 X5 3.0 247,000 miles
2004 325i 109,900 miles

It is now at the shop. I do believe it's something with the expansion tank or oil cooler, or both.

If this thing lasts two more years without self destructing (something major like trans or engine) I will consider it a good life. I was originally hoping it was just a hose somewhere, but it's just not worth me diagnosing knowing that the trans most likely needs to be flushed anyway.

Thanks for the replies and I'll update whenever I hear back from the shop.

Good timing. The upper radiator hose blew apart and as someone said, the coolant just went everywhere and soaked everything, along with obviously the system no longer being pressurized. I'm going to have them fix some other minor things unrelated and see if I can get the car to last another year or two (honestly shouldn't be a problem). Then it should finally be time for a new X5.

Good to hear it wasn't something serious!

Yeah, sounds like could be coolant in the trans, but there's plenty of hope the trans is still good. Good luck, hope you don't have to part her out.