Hello, Anytime I drive my Prius around town it drives perfect. The moment the Prius gets over 70 mph the overheating icon comes on the screen. Then I will get in the slow lane and let it get into the 60s and it goes away. I have taken the car to the dealership and they replaced plugs and wires. They told me they did not know what the cause was and that it could be anything from needing heads to the water pump. The vehicle has 260,000 miles and has had all routine maintenance at the dealership. Thank you so much for your help!