Dynamometer, also known as dynamometer, is mainly used to test the power of the engine, and can also be used as a loading device for gearboxes, reducers, and transmissions to test their transmitted power. It simulates the load conditions under actual working conditions, measures the output power, torque, speed and other parameters of the device, and calculates its performance indicators such as efficiency and energy loss. The main purpose of a dynamometer is to evaluate the performance and reliability of power devices, provide data support for engineers and designers, optimize design and adjust parameters. Dynamometers are widely used in fields such as automobiles, motorcycles, ships, and airplanes, and are one of the important technological means in modern industrial manufacturing and transportation. The working principle of the dynamometer is based on Newton's second law, which states that F=ma and force is equal to mass multiplied by acceleration. Drive the tested equipment to rotate through an electric motor, while measuring torque and speed. The measured torque and speed can be used to calculate parameters such as power and efficiency. Dynamometer is an indispensable and important part of engine testing. When the test runs continuously for a long time or the test environment temperature is too high, the coil temperature of the dynamometer will self protect and cause the test to suddenly stop. This not only delays the test progress, but also seriously affects the lifespan and performance of the engine and dynamometer. The host converts the absorbed power into heat, which is carried away by the flow of cooling water to ensure the normal operation of the product. When the water temperature exceeds 60 ℃, it will accelerate the corrosion and scaling of the parts, and in severe cases, it can damage the dynamometer. It is recommended to use a circulating cooling system with a heat exchanger in order to use treated cooling water. And a filter screen should be added at the water inlet. The dynamometer is equipped with a temperature monitoring alarm to ensure that the water temperature is not too high.