My friend was having issues with overheating and decided to change thermostats. Before installing the new one, he decided to test the old one. He put it in water on the stove with two thermometers. A digital and a mercury. The old thermostat worked as it should right at about 180. The new one wouldn't open until 220, so he exchanged it. The second new one opened at just under 200 and they were all 180. Many variables at play. From my experience, a head is a more reliable place to get temperature because the temp is less suseptical to change and represents the temp at a critical area. Also, be sure to place the sensor where it will always be imersed in fluid. The thermostat housing isn't my choice. I prefer 180 over 195, but that depends on climate and the particular build. I also like to install a manual over ride switch in electric fan systems so I can turn the fan on if I feel it's running hotter than it should. I've had sensors fail. On my iroc, I had dual fans, they were on seperate sensors. One came on at the set temp, the second came on at a higher temp so if the primary fan wasn't able to do the job, it came on, but didn't over drain the electrical system. This can also be done with two speed fans. Personally, I prefer manual cooling fans, but that depends on the build.