I used a
thermal snap switch with the brass probe. The probe is pushed between the fins of the radiator. I mounted mine below the radiator's inlet from the thermostat. The instructions say to mount it where the coolant temp is highest in the radiator. You can see the backside of the switch in the photo of the fan mount. The switch controls power to the relay. The one I used (Amazon link above) came with all of the parts to wire the fan. Because I have dual batteries in my Sporty, I opted to run the fan off the aux battery and powered the snap switch from it too. It allows the fan to run after the ignition is off, which it will do for a few minutes after shutting the engine off on hot days.
As for the shroud, I had concerns too. But the fans of this type all have thin shrouds around them. As long as you mount the fan so the body of the shroud is pressing against the radiator core, it will work fine. The mounting system I used puts a little pressure on the fan when the bolts are tightened up, pressing the fan against the radiator core. I did put the small foam pads that came with fan for mounting between the core and the shroud, just to guard against rubbing, though the mount is pretty sturdy.
My engine actually seems to be running cooler than before. But that was only realized after my old thermostat started to fail, I think because it was sitting dry for a week or two during the upgrade. That manifested in a series of temperature spikes that I attributed to the new fan. When the t-stat eventually got stuck closed, I realized what the problem really was and popped in a new one. Since then, the factory gauge has been sitting at the same old position it ran at with the stock fan, or just below while driving. By the way - that wiring of the fan to run with the ignition off actually saved my <img src="/forums/images/graemlins/butwiggle.gif" alt="" /> when the t-stat failed for good. It pulled the coolant temp down to the normal range a few minutes after the engine was shut off. I've seen the coolant temp rise after cutting an engine because the pump stops circulating the fluid and the heat of the engine is held in place. And my gauge was sitting just below the "H". I was a bit impressed that the fan could still pull heat out of the system with no circulation as quickly as it did. And the temp that day was around 100 F. Anyhoo, so far, so good...
<img src="/forums/images/graemlins/patriot.gif" alt="" />
