That is the A/C fan. It only is supposed to turn on when the A/C compressor is running.

If you have all the OEM shrouds in place, you don't need that A/C fan to do anything.

HOWEVER, what I do every time I swap a SR, is remove the belt-driven fan completely, along with all of the shroud crap. I leave the A/C fan bolted to the radiator (an OEM radiator is fine)....and then I pull the A/C fan relay out, and jump two of the terminals. This makes the A/C fan come on whenever you have the key in the ON position. So basically, the whole time you're driving. It it more than enough cooling for the engine to operate normally.

If you're really afraid of removing the belt-driven fan, you can leave it on there, too. But it isn't necessary and you can gain a few hp by getting rid of it.

In this pic, you can see my fusebox, where I have removed the A/C fan relay, and used a short length of wire (with a blade terminal connector at each end) to jump the terminals). My car has never even come close to overheating with this setup.