Hi Fred.
Which sensor on the radiator was replaced? The one on the right side of the car is the temperature switch for the aux fan and it can be confused with many other things.
http://www.realoem.com/bmw/showparts...99&hg=17&fg=05
I've not replaced one on an M50 powered car, but #13 on that diagram is probably the faulty component, while #10 is what I mentioned above.
Good luck!
best, whit