i had the same problem with my civic...once u rev the engine, temp needle would go down...
i remember i drove it like that for a while..i drove to macon and on that str8 highway rd, everytime i would go on top of a hill, it would climb down, and when i went down the hill, the needle would climb back up...
i eventually got it replaced...no engine damage from over heating
d16y8s rule!!