What is the function of the oil filter anti-drain back valve?

The oil filter anti-drain back valve plays a crucial role in maintaining oil pressure and ensuring efficient lubrication in an engine. This valve is designed primarily to prevent oil from draining back into the oil pan when the engine is turned off. By doing so, it keeps the oil filter charged with oil, which is essential for quick lubrication when the engine starts.

When the engine is not running, the absence of oil flow can cause the oil to drain back into the pan, leading to a delay in the delivery of oil pressure upon starting the engine. The anti-drain back valve mitigates this issue by keeping the oil trapped within the filter, which allows for almost instantaneous pressure buildup when the engine is started. Consequently, it significantly reduces the time it takes for oil to circulate throughout the engine components as soon as the ignition is turned.

Therefore, the functions: keeping the filter charged with lube oil, ensuring instant oil pressure, and preventing oil from draining to the oil pan, all contribute to the effective operation of the engine. Hence, the comprehensive nature of these functions justifies the answer as encompassing all the elements described, making "all of the above" the correct choice.