engine overheat

I finally got my z engine temperature under control. The radiater was checked by a repair shop and they said it was not flowing enough. I wound up with a new radiator,new water pump and new thermostat and new antifreeze. I also had installed a new temperature sender and even though the engine is running cool the sender pegs the needle. I had this problem with my old sender and wound up putting a series resistor in line with the sender to make the needle run normal. I checked the antifreese temp with a submersible thermometer in the top of the radiator and it read between 160 and 170 deg. F. If any one out there knows anything about the properties of this sender please let me know. If I can locate a schematic I may be able to figure it out.

Al S