Which statement is true about older AC motors during operation?

The statement that older AC motors have minimum resistance at high speeds is true in the context of their operational characteristics. As AC motors, particularly induction motors, run at higher speeds, their rotor experiences reduced slip, resulting in lower reactance and, consequently, lower impedance. This means that the current drawn by the motor is more efficient at high speeds, allowing these motors to operate smoothly and effectively under certain conditions.

In addition to this, it's important to note the operational dynamics of AC motors. While an older motor may still perform effectively at high speeds, its performance can vary at lower speeds due to increased slip and mechanical factors such as wear and tear.

Other statements such as high torque at low speeds, decreasing efficiency with age, and the necessity for constant lubrication, while potentially applicable to certain scenarios or types of motors, don't accurately reflect the typical characteristics of older AC motors during operation. These points focus on the broader implications of aging equipment or specific maintenance needs rather than the direct operational behavior at various speeds.