Discount sells a rad fan controller for 40$ that can be externally zip tied to the hose/housing etc..
Reduces leak points and can be set to come on and off over a wide temp range.
Regarding thermo siphon ,as long as the hot oil line runs up hill a little and is at or under the upper level it will flow. Mount the cooler so that the hot oil flows up hill . You do have to bleed it out a little as an air bubble will slow it down.
The ring gear cranks it along pretty well , esp synthetic that I assume you are using.