This is usually related to electronics in the car since they are what controls the fuel mixture once you reach operating temperature. Things to check are OVP, O2 sensor, Fuel mixture, I had the same problems also but not to this extent and the fuel mixture was the problem. Cloged fuel filter will usually cause problems constantly warm up or not. Also check for any vacuum leaks in the engine, justlisten for hissing and do a good visual inspection.
now back to work
xp