However it would eventually get to normal operating temperature, though it would take longer to get there. Since he describes driving for extended periods of time and experiencing overcooling, it's probably not the thermostat. If he drove 10 minutes accross town, then yeah, I'd guess thermostat.

 

Call Honda and find out if 170 degrees is the proper operating temp for your engine. If so, your thermostat is working and the problem is with the temp sender / temp gauge electrical circuit (see below).

For comparison, image your temp needle is the minute hand on a analog clock:
hot = 7mins past the hour
mid of the range = 15mins past
normal operating temp (for my '90 crx si, no mods) = 18mins past
cold = 23mins past
not registering (first startup of the day) = 25min past

So, your gauge gets to 22 or 21 and that's all?

Hmmm
-the radiator's working properly (hot coolant from top hose becomes cold coolant out of bottom hose)
-water pump works (coolant flowing)
-thermostat (working)
-temp sensor to gauge (could be bad; also check the wire connection to the sensor for corrosion on the sensor's lug/wire connector, loose connection between the lug and connector, or bad wire connection to connector)
-temp gauge might not be calibrated correctly (unlikely; bad connection to gauge cluster?)

When car is warmed up and the heat is turned on do the heater hoses get hot (170 degrees) like your top radiator hose?
-if they do, I bet the heater air deflector door isn't adjusted correctly or disconnected (it's moved by a cable that's connected to the heater knob) and the temp sensor / temp gauge electric circuit isn't working properly.

 

I'm printing the threads and will bring to my mechanic.....Will post result..lack Honda thermostat seems to get the most votes....but nobody can believe that 3 thermostats could be bad. Thanks again. cwo