My civic was doing that. After I had it Converted from auto to manual(An extra opening was cut and never used). Try riding with the windows up for a minute, and see if it stays at a normal temp. Then crack window/roof and see if it heats up the floor. If so you definately have a open in your floor board. Shiit you might could just get the car on a lift somehow and find it that way. The only way I fixed it was to just weld it shut.