I have a 1992 325i , 5 speed , 4 door sedan. It over heats at random. I'll be driving down the road just fine and all the sudden the heater will start blowing cold air and the car will start overheating. If I turn the fan off and on a few times it will usually cool back down , but not all ways. I took it to a mechanic and he said it was the fan clutch. My gut tells me he's wrong. Please help !!!