When should you close the drain while adding new oil to the system?

Closing the drain once the oil pouring out becomes clear ensures that you have removed the majority of the old, degraded oil from the system while allowing the cleaner oil to circulate. This method is beneficial as it indicates that most of the contaminants and sludge have been expelled, leading to a more effective oil change.

Allowing the old oil to drain until it runs clear means you are giving enough time for all the impurities to leave the system, which is a crucial step in maintaining the efficiency and longevity of the equipment. This practice helps in improving the performance of the system by ensuring that newly added oil mixes well with the existing fluid, providing optimal lubrication and protection against wear.

Draining the oil solely based on the timing of pouring new oil or pressure drops can lead to incomplete oil removal, potentially leaving behind contaminants that can affect the system's operation.