So my temp. guage goes all the way up when im at a stop light and then goes back to normal as soon as i start moving. I am going to replace the thermostat and replace the coolant tomorrow. If this does not fix the problem what else could the problem be?

 

sounds like the fans notturning on. do a search....

 

You can easily test the fan by turning your key to the ON position (car not running), unplug the fan switch sensor and jump it with a paperclip. If the fan turns on, you know it's working. I highly doubt this is your issue though.

I'm willing to bet its the coolant temp sensor

 

I didn't realize it said "as soon as I start moving...." My bad.