optimal running temperature

[JackFish]

I'm installing an electric fan.
Would like to choose a temperature sending switch that will provide the "best" running temperature.
I found one that's on at 210° and off at 195°.
Ideally I would put one in with a variable controller that allows you to adjust the on/off, and test and tune, but I'm trying to be frugal at the moment.
Any opinions or suggestions on this?
Anyone got one they would part with?
Is there maybe some way to use the existing sending unit?

 

[Explorer]

Here is one that lets you pick temp of sender. Can also use toggle switch for manual control.
http://www.centechwire.com/catalog/acce ... /fc3.shtml I've also seen the variable ones on E-bay, browse the electric fan section. Might check parts yard for one, maybe out of a Ford Taurus.

 

[JackFish]

Cool, thanks.
Oddly enough, the fan is from a Taurus.