How do I get my temperature gauge to read correctly?

Hello, It sounds like a problem with the engine coolant temperature sending unit (temp sensor). Look at the voltages going from the sending unit when the engine is cold, and when the engine is hot, and I bet they will be the same. However, you want to look at the voltage going to the unit as well. If the temperature sensor sends an increasingly higher voltage as the engine is warm, it is time to inspect wiring and test the gauge.