I have this recurrent problem with my 2002 Honda CRV. Last year my temperature gauge started acting up. It would remain at 1/2 mark after warming up but while driving it would sometimes go all the way to 0 and then come back up till 1/2 mark. It continued for some time and after a couple of weeks the check engine light came on with the error code P0118.
I then had the ECT sensor replaced. However after a few months the same behavior started with the temperature gauge and i again got the P0118 error code. This time i had the circuits checked at the dealership and everything seemed alright so i replaced my thermostat and also had the ECT temperature sensor replace (it was under warranty). This was a few weeks ago.
Now, since yesterday i am again seeing the temperature gauge fluctuating from 1/2 mark to 0 (cold). The check engine light hasn't come on yet. Could someone please tell what is going on? I'm at my wits end with this recurring problem.