Thermostat MISHIMOTO or OEM Honda

Stop using cheap thermostats. Get an oem honda unit and it will last and work correctly.

Your temp gauge is reading low because your mechanic is not using an OEM Honda thermostat. An OEM thermostat is designed specifically for your engine and the car will warm up quickly and the temp gauge will sit at the 50 yard line in any weather.

I replaced the thermostat with a Mishimoto thermostat and vaccume filled the coolant. I did a 30 min test drive in the 95+ weather with the AC cranked. Never went past the 7th dot.

The Honda thermostat opened probably 50% more than the aftermarket, so lesson learned there.

I got a bad mishimoto thermostat with similar results.

I bought and installed a Mishimoto thermostat that activates at 68°C, while my vehicle OEM (Original factory) thermostat activates at 88°C and fully opens at 100°C. With the Mishimoto thermostat (68°C), the coolant temperature basically stays 71 ~ 74°C when driving, from OBDII reading. Short Term Fuel Trim was OK, between -10% and +10%. I checked the spark plugs after one week, they were fine.

However, after three weeks (last Saturday to be precise), the Check Engine Light was on when I started the vehicle, and OBDII gave Code P0128. I searched the code online and got: coolant temperature fails to reach the proper operating temperature, or Coolant Temperature Below Thermostat Regulating Temperature. My thinking was the engine finally realized that the temperature was below the operating temperature, due to the Mishimoto thermostat.