I'd be checking the operation of the water temp sensor, if your not leaking coolant and the motor gets hot while driving, this is very strange.
Wouldnt the water get hot while idling, due to lack of air flow.
When the temp rises, feel the temp of the radiator cap, if it almost burns your hand off then you have a problem, also listen for boiling water, if your temp is that high your water/coolant will be boiling.