what might be my problem?

[koUki20]

everytime i rev past, i think 3,500. the temperature needle goes down. but once i rev back down less than 3,500 it goes back to normal. would anyone happen to know what the problem might be? it just really bothering me cause i know thats not normal. and also my "check engine light" isnt on.

[Kenrik]

check your coolant sensor.. if it's messed up strange things can start to happen...