i was just about to ask about a very similar thing.... im installing the thunderbird fan and need a temp switch to control my relays . i was thinking about one of these
Hayden Automotive 3652 - Hayden Electric Fan Controls - Overview - SummitRacing.com
but not sure if that would be right for temps or not. id rather not have one of the ones with the adjustable ****. id rather have a sealed unit like this one.

the controller is the last thing im missing for my swap.