Received the replacement coolant temperature sensor and finally checked its calibration… well, let me back up.
An authentic Honda coolant temperature sensor is roughly $45 online, and me being a cheapskate, looked for alternatives. Found one on Ebay for about $8, with the picture showing the sensor next to an authentic Honda part bag with the correct number on it. I knew better than to think it was actually what the picture portrayed and bought it anyway. Sure enough it arrived in a plain box with no markings whatsoever, so no surprise it’s a knockoff.
Boiling water in a Thermos was placed in the engine compartment where the wire harness could reach. The new sensor was plugged in, and it and an accurate mercury thermometer were submerged in the hot water. The sensors were allowed to settle for several minutes and then the temperature read; the thermometer settled out at 91C, while the sensor read 77C. Sigh, it wasn’t expected to read exactly right but this is kind of ridiculous. To be fair, I don’t know how accurate an authentic Honda part is, but doubt it’s that bad. We’ll see since a “real” sensor has been ordered.