What kind of temperature gauge? If it is a bodily thermometer, the thermometers probably have a maximum temperature they can actually measure, that or whoever designed them knew that above a certain temperature you would just be dead, and thus instead of reading 150 degrees it just says hot. I can't think of another thermometer that would just read out "hot".
temp gauge is stuck on hot
you could have abad temp sensor
A faulty temp sending unit can do that.
no way
Test gauge function with a mechanical gauge to get actual engine temp.
Low on coolant or a sticky thermostat, replace it.
normally the gauge should be in the middle.(between hot and cold) that is concider operating temp.
This would indicate that the system is low on coolant when the gauge is hot. Not enough coolant to service the heater core.
Your temp. sensor might be faulty, or the wiring for the gauge, but 9 out of 10 times this indicates air in the cooling system. Check the overflow tank. When there is HOT coolant on the sensor, it pops up. When air hits the sensor, it dives down.
Replacing the gauge could be a costly job but it is seldom the gauge goes bad. More likely the temp gauge sending unit is at fault. Replacing the temp gauge sending unit would take less than 15 minutes.
Broken Temp guage
If you don't have a temp. light, or temp gauge, then just install one.