Borg Warner temp. Switch TFS-521 is what I used to turn my fan on and off. On at 195-200 ascending and off at about 180 descending. I drilled and tapped the top of the thermostat housing, I think to 3/8 NPT, and then used abushing to reduce as the temp switch is the next size smaller, I think 1/4" NPT. Painless also makes a switch.
I ran no t-stat last summer for the first 500 miles on the new enging following the builders lead. The electic fans only came on at a stop in traffic or very hot run times but for a very short period.
Added a 180 t-stat over the winter and now the electric fans will not shut off? Just added the 200 on 185 off painless temp switch and still no luck. With all the talk about exploding fans I hate having them on when not needed?
I'm running the Borg Warner (BWD) switch with a 180 thermostat and my fan comes on only in heavy stop/go traffic or sitting still. Unplug the temp switch and see if the fan goes off. If it stays on, the problem is in the wiring. If the fan goes off, the switch might be bad. Check the switch to see if it is grounded to the block when cold. If it is, the switch is bad. I'm assuming that the Painless switch is used to ground the fan relay when the temp. gets hot enough. We have had to replace two of the BWD TFS-521 switches because they went bad, but they failed such that the fan would not turn on. Good luck.
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