Temperature norms for I6

[hevymetl]

Pretty sure I have a 250ci I6. The po had installed an electric fan controlled by a tstat sending unit that doesnt seem to be working. When I ground out the lead the fan goes on but left on the sending unit, it does not. If left to idle, the stock guage will eventually climb to at least 3/4s of the way to "H". I guess Im trying to figure out a few things at once. What are the corresponding temps vs. position of the needle on the guage? How do I know if that sending unit is or isnt working properly? Should I just pop off the tstat housing to check what tstat is in there for ****s n giggles? There is no shroud on the back of the radiator as well.
Thanks in advance, John.