What is the function of the anti-drainback valve in a lubrication system and what happens if it fails?

The anti-drainback valve in a lubrication system prevents oil from draining out of the oil filter and engine's upper galleries when the engine is shut off. This valve is typically located within the oil filter or in the oil filter adapter. Its primary function is to maintain oil pressure within the engine upon startup. When the engine is running, the valve is open, allowing oil to flow freely through the filter and into the engine's lubrication pathways. When the engine is turned off, the valve closes, preventing oil from flowing back down through the filter and emptying the oil passages. If the anti-drainback valve fails, oil drains out of the filter and the upper engine areas while the engine is not running. Upon the next startup, it takes longer for the oil pump to refill the filter and pressurize the lubrication system. This delay results in a period of oil starvation, where critical engine components, such as bearings, camshafts, and valve train components, are not adequately lubricated. This oil starvation can lead to increased wear and potential damage to these components over time, especially during cold starts when the oil is thicker and flows less readily. The most noticeable symptom of a failing anti-drainback valve is often increased engine noise, such as valve lifter ticking or rattling, during the first few seconds after startup. This noise diminishes as the oil pressure builds. In severe cases, prolonged oil starvation can lead to premature engine failure. Using a high-quality oil filter with a reliable anti-drainback valve is therefore crucial for maintaining proper engine lubrication and prolonging engine life.