I got some bosch 75amp continuous duty relays and used the flex-a-lite controller to switch on the low speed and a manual setting for high and off. Lots of opinions on the probe type controllers but they are cheap and effective and adjustable. Got my relays here for about $18/each. ww.solarseller.com
I had considered a temp switch setup in the water flow but there were no avalable openings plus those switches are only accurate to within 10-15 degrees wich is a potential swing of 30.
Last consideration, for me anyway, was that I have an auto transmission. Meaning that when fan is not running the transmission cooler is not getting air so it can run a little hot. I am thinking to do a smaller fan for just that eventually.
"The right to be heard does not necessarily include the right to be taken seriously." —Hubert Humphrey
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