I have a 99 neon DOHC that I noticed the temp gauge went all the way the top for a second and then cooled right back down. I week later the temp would rise a little then drop back to normal. I replaced the thermostat and the problem went away for a month. Now the gauge went all the way to the red again and stayed and then came back down it also rises about half way then drops. Anyone have any suggestions, I have already replaced the thermostat and the fluid level is fine.

 

You may have an air bubble trapped in the system. While the engine is cool, take the "rad" cap off and then start the car. Let the system circulate for a few minutes. This should allow the air to escape.

Either that or possibly a bad CTS.