BMW: cooling system??, bmw e30, fan blade

Question
BMW E30 1988 318I.. THIS CARS TEMP SAT AT 3QUARTER MARK SO I CHANGED THE WHOLE COOLING SYSTEM EVEN DOWN TOO THE SENSOR.; I ALSO HAD HEAD CHECKED AND THATS FINE"!! AND IT STILL RAN AT 3QUARTER MARK!! JOSH TOLD ME TOO GET ANOTHER THERMOSTAT. SO I DID FROM BMW GARAGE,I ALSO GOT ANOTHER VISCOUS FAN COUPLING ITS ALOT BETTER BUT STIL IN BETWEEN HALF AND 3QUARTER MARK STILL NOT PERFECT SURELEY IT SHOULD NOT MOVE FROM HALF MARK.. ANY ANSWERS?  

Answer
Josh,
It is anyones guess on this one. Electric fan may not be working right? Any one of the 5 tempsensors? Clogged head or throttle cooling passages? Clogged cooling hoses under the manifold? Maybe the gauge is just wrong, E30 cars are not known for having the longest lasting instrument cluster. Or maybe the thermostat just got put in backward. Maybe the fan blade is on backward, I see that plenty. I like to flush E30 radiators with CLR since they generally get calcium clogged pretty easily.