Driving today the temp gauge jump all the way to reline. Pulled over and shut it off and popped the hood no leaks and didn't seem to be that hot. Started it back and still showed hot for a few seconds then came back down to normal. Drove another 10-12 miles and then it jumped to redline again. Still no leaks. Got home let her sit for a few hours. Checked the radiator and it was full. Crank it up cold and it temp gauge shows pegged all the time. Any idea's????