Hi I've purchased a 2008 1 Series a few months ago. Recently it's been overheating. I've noticed that the car reaches operating temperature normally, then suddenly the heater stops blowing hot air, and only blows cold air instead while the temperature quickly reaches over 110 degrees. Then it'll suddenly drop back down to 90 and the air will be hot again. Anyone know what it could be? I've checked for errors none stored. Water pump has been replaced recently. Mileage on 102k. Garage appointment booked for tomorrow. Apologies for the long read.