This Derale 18735, 180 degree Single Stage Electric Fan Controller, automotive radiator coolant electric fan thermostatic switch, is a complete piece of junk. I tested the switch by placing it in 200-degree water, not excessively hot but above the 180-degree, "preset turn-on temperature", for 10 minutes. I used a coffee cup, hot plate, food thermometer, and an Innova digital continuity tester. I tested it 5 times and it NEVER came on. Unfortunately, I did not find other reviews of this product until after I had ordered it. In several Jeep related off-road forums, and a couple of drag race forums, I found several complaints of faulty Derale products, from ALL of their fan controller product lines. Mine turned out just like the other complaints. I will not buy a Derale product again.Additionally, the product box and the Derale product website, both claim this product comes with a 3/8" NPT plug for mounting in the engine water jacket. However, #1, the plug is actually metric, #2 it is not threaded in NPT, and #3 it is almost 5/8" of an inch in diameter, NOT 3/8", like the OEM Coolant sensors.