My 99 Mercury Sable Le, v6, speedometer died yesterday when I was driving 30 mph. The car continued to run although a bit sluggishly. I then stopped. I had driven the car for only 5 minutes but the heat gauge remained at normal midpoint for an hour before declining. After several hours, I resumed driving and all seemed well. There is a precedent to this problem. A month ago, I was driving 55mph and the speedometer fluctuated wildly from 0 to 50 or 60. I again stopped and after an hour resumed driving without a speedometer problem until yesterday. In neither instance did the engine repair light appear. What’s going on with my Speedometer and Heat Gauge? This is a “Puzzler.” Please help me solve it.