This gage shows the engine coolant temperature. If the gage pointer moves into the shaded area, your engine is too hot.
This means that your engine coolant has overheated. If you have been operating your vehicle under normal driving conditions, you should pull off the road, stop your vehicle and turn off the engine as soon as possible. (The larger tic marks are in increments of 30° below 220°F (104°C) and in increments of 10° above 220°F (104°C).)
See Engine Overheating for more information.