Originally Posted by DansM
^i hear the AA pulley is designed with intension to not allow the engine temps to increase..... I could be wrong, but that's what I have read.
I think this engine still has a belt driven water pump, so the pump is slowed down and pumps less coolant when an underdrive crank pulley is used. That result is undeniable. Whether pumping less coolant than BMW designed affects engine temperature is debatable. Probably under most circumstances, coolant temperature will remain unaffected.
I have an underdrive crank pulley (not from AA) and am not worried. On my E36M3, I used to run an underdrive water pump pulley, but changed to a stock size pulley since I have more than doubled engine horsepower and torque and thus dramatically increased thermal load on the engine. If my E90M3 with the usual NA mods was a track car, I might be concerned about its cooling ability under the rigors of sustained high rpm use on the track.