Thanks for the responses.

I checked the coolant this morning and it was still good. The indicator stick was at the max level. I didn't have any puddles under the car either.

I'll start looking for that heater control valve tonight.

BTW, this probably has no bearing on what I'm seeing, but when I have the temp adjusted down low, I always turn the flow know to the 3 blue dots. When the heat is on high, I always rotate the know to the 3 red dots. Not sure if any of this matters.

Also, can anyone recommend an independent repair shop for BMWs in the southwest Houston area? Sugar Land would be even better! Thanks.