[trularin]

May I suggest a small test?

Take the T'Stat and put it in a pan of boiling water. If it opens, Completely, it may not be the T'Stat.

The hole should be no bigger than 1/8" as stated by BIB, The rating is a matter of choice, however, you might want to select a 180 to 190 degree unit. Installed with the point towards the radiator.

If you have a tank on top of the engine, I think you can see if the coolant is flowing once temperature has been reached.

I Like the idea of the IR thermometer. Thermo-imaging would a whole bunch better.

Did this just start or are you just getting the engine up and running. More history would help. If this is a first time run, you may have other problems that go beyond the T'Stat.

Just my $0.02