If you say that someone is temperamental, you are criticizing them for not being calm or quiet by nature, but having moods that change often and suddenly.
He is very temperamental and critical.
他喜怒无常,而且吹毛求疵。
If you describe something such as a machine or car as temperamental, you mean that it often does not work well.
The boys couldn't start the temperamental motor.
那些男孩子无法发动那辆性能不稳定的摩托车。