If the main oil filter becomes clogged, which valve allows unfiltered oil to lubricate the engine?

The filter bypass valve is designed to ensure that the engine continues to receive oil even when the main oil filter becomes clogged. When the oil filter is functioning normally, oil passes through the filter, where impurities are trapped, ensuring that only clean oil circulates through the engine. However, if the filter becomes clogged and restricts oil flow, the filter bypass valve opens due to the difference in pressure. This allows unfiltered oil to bypass the filter and continue circulating through the engine to maintain lubrication, thus preventing engine damage from lack of oil.

This functionality is crucial for the engine's operation, as it provides a safety mechanism that prevents failure due to oil starvation, even at the cost of introducing unfiltered oil into the lubricating system temporarily. Other options do not serve this specific purpose; for example, the pressure relief valve deals with excessive pressure in the oil system rather than bypassing filtration, while the return valve and oil inlet valve do not facilitate the flow of oil when the filter is clogged.