Ha! That sounds familiar! Flip flops... Every mechanic should have a pair!
How many miles do you have on your car? Have you ever had a coolant system flush? If you have a lot of miles on the car, it is possible that you have a blockage in your radiator. The failed cooling fan clutch is also a strong possibility. If you aren't getting any milky residue or black grit in your coolant resivior, I would lean towards either the fan or the blockage in the radiator. When the car is cooled down, open the radiator cap and see if you have a lot of white build up on the inside of the radiator. If you do, you seriously need a good system flush.
Remember, always start with the simple stuff first as that is usually what goes wrong first... Also, if you have a bad radiator cap, your cooling system won't keep the correct pressure in the cooling system and cause it to over heat.
1997 E36 M3 - running stocker style right now...