Hi, I own a ML420 with 35000miles on the clock, I have just noticed that after driving it for around twenty miles the cooling fan cuts in. Once it cuts in it will not cut out. It always does this even though I have been driveing on open roads and not stopped in traffic. The engine does not appear to be warming up too quickley and the coolant level is correct. Please can anyone offer any advice or even let me know if this normal.