Which is a sign of proper maintenance regarding engine oil?

Regular checks and timely changes of engine oil are essential practices that indicate proper maintenance. Engine oil plays a crucial role in lubricating components, reducing friction, and dissipating heat. By routinely checking the oil levels and condition, mechanics can ensure that the oil is functioning effectively and not becoming contaminated. Timely oil changes prevent the breakdown of oil and help maintain engine performance, as old or degraded oil can lead to increased wear and the risk of engine damage.

The other options do not reflect best practices for oil maintenance. Changing oil only when it appears dirty may lead to neglecting oil degradation before it becomes visibly contaminated. Monitoring oil color without changing it ignores the necessity of assessing oil performance, which can deteriorate before it looks dirty. Filling oil only when the engine is running can lead to inaccuracies in measurement and potential engine risks, as it is best to check oil levels when the engine is off and has been allowed to settle. Proper maintenance encompasses regular monitoring and timely interventions, thus ensuring the longevity and reliability of the engine.