Temperature Sensor?

Hey guys,

I was out driving my car today, and this is the first time I’ve noticed this problem. When my hits around 3 - 4000 rpm, the temperature gauge goes crazy, its drops way down to C. I assume its the sensor thats gone, but I have no idea how to check it. I’m not much of a car guy but I’m learning so I was wondering if anyone could help figure this problem out, and how I can go about fixing it myself.

Thanks alot

Can no one help me?