quote:My pressure tank has a 4th connection for a sensor
That was the original location of the temp gauge sensor.
It was not a good place. If the water level should ever drop below that point, easy to happen with a leak, the sensor would only be measuring air temp, not coolant.
BIG trouble would no doubt follow, as the gauge shows nothing wrong. But the motor is fast on a suicide journey.
Most owners have long ago moved the sensor to the proper place in the block, below the thermostat housing.
Larry