If your car is overheating with the AC on, but is OK without AC. Then I beleive that it could be one of two things. 1) the aux fan switch that is mounted on the radiator. Older E30's have two switches (Lo/Hi). Later E30's have one switch that does both Lo and Hi. There is a good testing procedure in the Bentley repair manual. 2) could be aux fan resistor. (follow link to fix procedure). I hope this helps, Alan Alfano 88 325iX