Which of the following is an indicator that a jack needs maintenance?

An inconsistent lifting height is a clear indicator that a jack requires maintenance. When a jack cannot maintain a consistent lift, it may suggest several underlying problems, such as hydraulic fluid leakage, internal wear and tear, or malfunctioning seals. These issues can compromise the jack's effectiveness and safety, making it crucial to address any irregularities.

In contrast, frequent successful lifts indicate that the jack is functioning properly. A standard hydraulic fluid color suggests that the fluid is not contaminated, which is often a positive sign regarding maintenance. Stable weight handling indicates that the jack is operating within its designed specifications and can safely support the intended loads. All these conditions represent the normal or ideal operation of the jack, whereas inconsistent lifting height directly points to a malfunction that should not be ignored.