With the dimensions given, I do not understand, other than the 261 housing holds more water. Inlets and outlets are identical.
However, since there is a second port, it makes me think the whole reason for it is because one of the ports is above the thermostat, and one is below. Maybe this allowed for more options in heater design? The one below (engine side of the thermostat) would be hotter quicker. No idea, just guessing.
I know nowadays guys want them for that second port to install an electric fan sensor. But 'nowadays' we have electronic thermistor solutions that do not require access to the water stream. If you have any ideas Tim...
