Because the gauge is broken.
get a new temperature sensor.
In very short: If the thermostat stays open, the warm-up time for the engine will be significantly longer, resulting in unwanted start-up wear. If the thermostat stays closed, the engine coolant can not circulate through the engine and cooling system, resulting in the engine overheating, as the coolant is used to keep the engine in a specific operating temperature.
Test gauge function with a mechanical gauge to get actual engine temp.
The temp sending unit or gauge is bad, probably the sending unit.
Your car engine isn't getting up to the desired temperature, about 130 degrees Fahrenheit.
probly bad gauge or loose wire buy a manual gauge one with the oil line right to the gauge nothing is wrong. the guage is supposed to be high when driving. it will drop when you stop or are idling.
Most likely cause is a failed engine thermostat.
You can tell your Xbox 360 is overheating when the fan stays on and sometimes when there is a red ring glowing on the console.
With no make/model/year/engine information to work with...The temperature gauge is driven by a simple sensor that is both cheap and easy to replace.Any auto parts store will be able to help you find it on your engine, and of course more than happy to sell you one.
Thermostat is sticking.
The needle is getting stuck at the top of the gauge. Take face plate off and bend the edge of gauge down so not to get stuck up There again! If the gauge is not moving then I would suspect that. If your car starts and runs and the engine gets warm and the radiator gets warm and you can get heat out of your heater then yoru thermostat is okay. Make sure your temp sending unit, which should be out near the thermostat housing, is connected. If you find it, pull off the connection and make sure the connection is clean. If you start the car and only the motor gets hot, do not overheat the engine. If the engine gets above operating temp and the radiator stays cold, then it may be the thermostat or a broken water pump.
The engine computer turns it on at start up for a bulb check. If it stays on the computer has detected a malfunction and set a code.