DOES NOT FIT DIESELS OR COOPER S (Big vent in front of bonnet). Radiator Expansion Tank Water Bottle Cap For MINI & ONE Cooper 2001 to 2006 Petrol. Never remove the cap from a hot engine, the cap may 'fly off' on releasing and hot coolant will burn your hand, if you must remove the cap, cover the cap with a suitable cloth, lift the cap slowly to release the pressure, then carefully remove the cap, do not put finger in hot coolant.