Cleaning water jackets 225

Was the engine well heated up? If the gauge was reading high at that time, then the gauge or sensor is clearly off. The thermostat was just barely opening if the t'stat housing was that cool, so that is an indication that things are flowing well. The temps drop to the lower hose sounds OK.

Go get a TS6178 sensor from NAPA and put that in and see how the gauge reads. That will cause the lowest readings of any common sensor used in that application. But even with that sensor, my gauge reads at the top of the normal range when on the interstate in 80-85 degree ambient temps but the coolant is at about 198 degrees so it is OK.