Hello all, first I will start by saying i bought my 2001 CRV with the temp gauge not working at all. I have since replaced the coolant temp sensor, coolant temp sender, and radiator fan switch with all new Honda sensors. When the car gets up to operating temps (190F) my scan tool reads properly, and the sender ohms out properly. I have confirmed the vehicle is at 190F by using a thermometer in the radiator coolant, and pointing a infrared gun at the temp sender/cylinder head. I have performed a resistance test on the wire going to the cluster from the sender, and also checked all grounds on the vehicle. My gauge currently will slowly rise to H (just before the red mark) as the car gets warmer, it doesn't go up instantly, just slowly rises. When i unplug my alternator (which is new and tested OK) the gauge reads normally, and when I turn ignition on (engine off) the gauge also reads properly. I get 12.4 volts at the cluster when key is on, and 14.4 volts when engine is running. I have also replaced with a used gauge cluster as I suspected mine to be faulty, but the issue was the exact same.

Parts replaced:
OEM coolant temp sensor
OEM coolant temp sender
OEM radiator fan switch
OEM thermostat
radiator
radiator fan assembly
second hand gauge cluster
alternator