(1) Hand touch: Touch the shell by hand without scald and the temperature of the motor is normal; If you put your hand on it and burn it immediately, it will contract and the motor has overheated(2) Drop 2-3 drops of water on the motor shell. If the heat does not make a sound, the engine is not overheated. If the wood evaporates quickly and makes a "cry for help", it means the engine is overheating.The correct way to determine if the motor is overheated is to use a thermometer. Motor overheating, should immediately stop inspection, find out the reason, troubleshooting before use.