One problem related to coolant leaking has been reported for the 2009 Mini Cooper S. The most recently reported issues are listed below.
I was driving down the highway and my car gave me a warning that my engine temp was way to high. I was lucky enough to have a good place to stop and check out whay was gong on. I open the hood, the engine is smoking and the coolant reservoir is neat empty. I look and see a pool of antifreeze coming from the thermostat. This is the third thermostat I have installed on this car and the second faulty one I have had in 3 months. This is also the second time I have had to stop on the highway due to a badly leaking thermostat.