i have a 98 cobra and it has a wierd over heating problem. when i hop in it and start driving the temp gauge stays on cold until i drive for about 5 or 10 minutes, and then it goes up gradually all the way to the farthest point of the normal. then it goes back to where it should be. i could drive for an hour and the gauge never moves again. it only does it when i first get in it from a cold start. i changed the thermostat and coolant thinking that the thermostat was just sticking, but obviously wasn't it. does anyone have any ideas?