My Range Rover will run hot, then I will turn it off for a minute, and start it again. The gauge will fall to the normal range within another minute. According to my scanner it will run at 235 and then climb to 250-260. Literally after 60 seconds of engine off, I can start my Rover and within another 60 seconds the temp is back to 225 or 230 degrees. I've seen it hit as low as 215. The coolant appears to be full. Any idea what could be going on?