The Stovebolt Site Forums The Shop Area Engine Shop Engine getting too hot before thermostat opens

What am I missing? If water pump is working correctly, and has proper level of fluid in the radiator when engine is shut down at operating temperature, block is completely flooded and water had been flowing across tstat. Now engine cools and is restarted. Water pump pressures up block water level to Tstat, but until block temp gets to 180 in this case, and special spring which expands at 180 elongates, opening passage and full circulation is once again achieved. I don't understand why having partial warmed coolant on the backside of the Tstat is necessary, unless it takes 220 deg to offset the cold backside and get the avg temp on the spring (or the entire tstat housing as Joe and Jerry say) to 180. That would be consistent with heater hose loop and the small hole solution.