After installing the temp sending in the oil drain plate, it always read low. My engine could be almost smoking hot, and the gauge still read 140 degrees F. So, I installed a T like the one on the left in the oil line coming out of my oil pump. This read a correct temp: about 200 when the engine was warm.

Note one important lesson: the photo on the left shows smooth connectors. These were really, really bad. They are not "hose barbs". I tried them because they have a larger internal diameter, however, my oil line blew off. Yep, it spewed 2 quarts of oil in a couple of seconds, and my oil pressure when to zero. Lesson learned. I replaced the smooth ends with real hose barbs. It worked, but threaded, high pressure fittings would be a better idea.