The problem with using the OBD II adapter setup is that OBD is for automotive (car and light truck) applications and you have a "truck" engine, so the OBD doesn't have the setup tables built in for your engine. Some of these scanners/adapters work, some don't.
Your best bet would be to buy a scanner designed for your engine.
The Scangauge D is inexpensive and will do what you want. https://www.scangauge.com/products/scangauge-d/
On the water temp, the dash gauges are notoriously inaccurate. You definitely want to verify the temp reading you are getting on the dash.