The average operating temperature of an engine is found by measuring the temperature of the thermostat housing with an infrared thermometer and should be between 180-200 degrees Fahrenheit. Various parts of the engine can reach different temperatures depending on their location and function inside the engine.
Vehicles come equipped with temperature gauges on their dashes. This is the easiest way to determine if the engine is at its ideal temperature. The needle will reach a point on the dial that is halfway between the hot and cold indicators in the dial. The needle will always start in the cold section of the dial and reach the median as the engine warms up. With proper cooling and maintenance, it will always stop rising at the same point on the gauge once the engine is heated.