| I have a Mini One D which has done 98,000 miles, its an 05 and has been serviced at the intervals recommended by a garage (not BMW specialist). I have had no trouble until I changed the air filter for a K&N panel filter, went on a long journey and the engine overheated. Added 2 litres of water to the cooling system initially, on return journey added a further 6 litres over course of journey. Car kept over heating, there is no obvious coolant leakage, oil level is normal, exhaust dry. Got home and checked all hoses, no leaks, left standing and running with news paper underneath. Concluded that it could be filter screwing up the engine management system. So changed back to a paper filter. However did note a slight hissing sound from coolant expansion tank cap.
I didn't experience any problems over the past week until today, when engine overheated again. Water has vanished again, topped up and left. No leaks evident. However today have been running aircon, I wonder if there is a link (aircon never serviced). Noted a comment on one of the threads about checking temperature of Rad, if the Rad is cool and the car has over heated then a good chance the coolant isn't being circulated through it, although ive noticed my hoses are quite hot and I am sure I can hear the pump working. Can anybody suggest anything, I havn't as yet taken it to a BMW specialist to get checked out, but may be my only solution. I am going to monitor over the next week and see if there is a link with aircon, may even change thermostat etc and engine temp sensor.  | 
