Overheating seems to be a common ailment, particularly for the six cylinder BMW. I suspect the cause is too tight engineering specs in relation to variations in castings in water passages. I cured the problem in our old BMW 2500A by insisting that our garage recore the radiator with a larger core. Unfortunately, the damage from overheating had taken its toll, and the poor dear expired at 90,000 miles (some 20,000 miles later) with a cracked head and piston. Our BMW 2002 has never given us cause for worry about overheating, nor has our BMW 530i.
But the 2500 overheated from the first. Countless trips to the dealer, multiple treatments (from disconnecting the automatic fan to boiling the radiator) failed to cure the problem. Recoring solved the problem entirely.
I suggest that anyone having regular overheating problems not waste time, energy, and money seeking other solutions but spend the relatively small sum necessary to have a larger core installed.
Author: Stephen R. Holman