My 250 always showed hot on the gauge, 220 +, I didn't have a heat gun to check at that time so I was careful about driving it to hard. It would idle around 190 or more with a 180 t-stat. I moved the temp probe from the head to the thermostat housing, right under the thermostat. The gauge now reads 180 +or - as the thermostat regulates. The original hole location was right between #1 and #2 cylinders and the probe was picking up head from the cylinder chambers. I don't care what the water temp is deep in the engine, as long as what comes out of the thermostat is right, all is good.
You might consider moving the temp probe and giving it a try.
Joe
