Can someone please explain to me why my temperature reads like this???

 

Clogged system, water pump not working well.

When was your last full system flush?

 

I don't think the temperature gauge keeps reading when the car isn't running, but I could be wrong.

GM had an issue with the stepper motors they used in their instrument clusters. It was a very common speedometer issue but I have seen other gauges with the same issue.