Last week, the yellow temperature warning started flashing on for a few seconds at a time. I took it in to North Scottsdale Mini yesterday and it was diagnosed as a creacked thermostat housing.
symptoms were: yellow temperature warning light flashing on briefly
This per my service advisor is relatively common

 

I had the same problem. They are replacing the thermostat housing as we speak....Do they change the oil and antifreeze after fixing this part? Is it possible of cross contamination between the two?

 

Coolant will be replaced, and no to the other question, they will not mix.