What is the typical consequence of running an engine with old oil?

Running an engine with old oil typically leads to reduced lubrication. As oil ages, it breaks down and loses its effectiveness in lubricating engine components. Fresh oil contains additives that protect the engine from wear, prevent corrosion, and help to keep it clean. However, over time, these additives become depleted, and the oil itself can accumulate contaminants such as dirt, metal particles, and carbon deposits. When this degradation occurs, oil ceases to provide the protection and lubrication necessary for smooth engine operation. This can result in increased friction among moving parts, leading to wear and potential engine damage over time.

While increased fuel consumption and improved performance might seem like plausible outcomes, they do not directly derive from the presence of old oil. Similarly, stronger combustion is not a consequence of aged oil; in fact, the overall performance and efficiency of the engine may decline due to inadequate lubrication. Thus, the core issue with running an engine on old oil is indeed the significant reduction in lubrication quality.