Thermostat, I had the problem in my previous EK hatch when I bought it. Replaced the thermostat and completely flushed the system and filled it back up and the car stayed at the proper temperature.
If the top hose is hot and the bottom is cool/not getting circulation then the thermostat is stuck closed.
__________________
Mazda 2 Forums
R.I.P. Pablo 'Fathead' Garcia - Love you man! See you on the other side!
R.I.P. Kevin 'Slo_Si' Gonzalez - You will be missed!