You may have to get creative with bench test, but it should be doable. The switch just provides a ground when it reaches a certain temperature. You can use a meter on the ohm setting. When you touch one lead to the wire stud on the switch and the other lead to the body of the switch, it should be open. Heat up the tip of the switch and you should have continuity.
The reason I suggested water on the stove is because you can heat the water and measure the temp to find out how hot it has to be to complete the circuit... that is, if the switch actually works at all.
Another idea is that you may have air in the system and the tip isn't getting submerged in the hot coolant. This would normally happen when the switch is located on the top of the engine. I actually can't recall where it is on the 2.3, so this may not be your problem. I do know these cars have issues with air in the system due to the radiator position vs the upper hose and intake. People have fancy ways to burp it, but I never bothered with that stuff. If i have to top off coolant, I just put a much as I can get in it. Run it till it reaches temp, then shut off. Make sure the overflow tank is in place and keep it full while it cools down. After the first couple drives, I'll keep an eye on the overflow tank during cool down and top off as necessary. I'm usually under the hood anyway, tending to other things.
