Final answer:
An obstructed oil cooler passage leads to reduced flow and increased oil temperatures, which can cause the oil to become too thin, reducing its effectiveness as a lubricant.
Step-by-step explanation:
If the oil cooler passage becomes obstructed, it can lead to a reduction in the size of the opening, which in turn creates turbulence. This obstruction can cause the oil to flow more slowly through the engine. Additionally, obstructions in the cooling system can affect the oil's ability to regulate temperature, leading to inefficient lubrication. Since engine oil must maintain a certain viscosity to properly lubricate engine components, any increase in temperature due to an obstruction can cause the oil to become too thin, reducing its effectiveness. This phenomenon is crucial since oil that is effective at lubricating a cold engine may not maintain its protective qualities at higher temperatures, thus compromising the overall health of the engine.