What temp of radiator fan switch?

[shortboxin]

I've got an '84 C10 that I'm just getting around to installing an aluminum radiator and electric fan in post 5.3 LS swap last September. From the sounds of it, guys are recommending using an external fan switch rather than rely on the PCM to control the fans for numerous reasons.

I would like to mount a switch in the radiator in an available port in the upper portion of the passenger radiator tank. The factory temp for the thermostat is 186°. Based on what I've read, you need to factor in that the water temperature will be lower than 186° due to the fact that it is mixing with other lower temp water. Then again, I probably don't want it turning on at the thermostat's opening temp, so maybe the 186° range in the tank will mean the water coming in is actually 195°? to get 186° at the switch?? I'm not actually sure this is even a viable option, but otherwise, I've got to go to the passenger rear head port or make something to go inline on the lower hose. Neither of which is a "good" easy option.

Anyone with engineering background that has some experience with this? All help is much appreciated!