Running cool

Sometimes after driving for a while, i notice that the water temperature needle might be on a little less than 90ºC (normal centre value).

My question is, why is this happening. Is my engine running cool or is their a problem with the water temp. sensor. Where could the fault be.. and is it bad?

Hows the fluid level? Seeing that the CTA costs a few bucks, I'd go ahead and just replace it... Have you checked the rad hoses to make sure they are up to temp? I wouldn't reply on the CTS if it seems buggy (I had this problem yesterday... temp rad fine, lower rad hose was cold)