my oil temp started acting weird today....starts at 100 then it went to 100 and then when I looked back at it...it was back down below 100....bad connection? bad gauge?

 

100->100->100???? Does it move at all? If not, could be bad sender, bad guage, or both. Also, what kind of car is this on? What kind of guage is this (since we don't have oil temp guages stock). Need more info and correct typing.
~Tom