Nip into natrad
But seriously does it go Immediately to hot when you start the car (within a few seconds?) ? If so electrical gremlin
If it takes a bit longer like normal warming up from cold and goes hot after a few minutes - then dont drive it. Get it checked out or the consequences will be serious,, if not already.
Youv'e checked the basics ?
Ie: is full of coolant, flushed it properly, refilled, no air in the system, waterpump working? Therrnostat as above