2008 E90 M3, 55,000 miles, check engine light is on and increased emissions is shown. I checked the gas cap and the performance of the car is fine. I took car into a respected independent BMW shop and they put the car on the computer and they tell me the thermostat is sticking open and the car is over cooling itself and the thermostat assembly needs to be replaced. Due to where the thermostat is located it will take most of a day to replace the assembly. As you might imagine, this results in a large labor charge (the parts are really not that expensive). Does this sound reasonable?