An exhaust gas, or EGT gauge, measures and displays the temperature of your car’s exhaust at a point in front of the catalytic converter. This gauge is necessary for engine tuners and those people that like to keep their car running as best as it can. If your exhaust temperature is out of an optimum range, it means that your engine is running too rich and has too much fuel for the amount of air it is taking in. Conversely, if the exhaust gas temperature is too high, then it’s running too lean, or has too much oxygen being burned for the amount of fuel that is being burned in the combustion chambers. A too lean condition can burn exhaust valves, so it must be alleviated as soon as possible. An EGT gauge will help with this.
For more info, see Types of Car Gauges