All good responses. I have a mercury thermometer that I stick in the radiator (cap removed, engine running) to verify actual temperature. Is a good way to verify if T-stat is working correctly, and tells the true engine coolant temp. So it verifies the gauge and thermostat are telling the truth and working correctly.
Just today, I worked on a car.. the gauge said 3/4 way to max temp at engine ide. Well, my trusty snap-on mercury thermometer said actual temp was 168 degrees, engine has a 180 degree thermostat. So now I know the dash gauge is wrong.
Removing T-stat would be a good easy to do test. Engine should run real cool then. If not, then food for thought: Did you install the head gaskets correctly?? They block flow at front of engine block passage and force flow to circulate thru entire block and heads.
Many factor thermostats have a small hole or one-way valve that lets air out of the system. Does your T-stat have one? If not, I always drill a tiny hole in T-stat, just outside of movable center portion so air can't be trapped so easily. Works real well, so as you pour in fluids, much of the air can escape before you even start the engine.
