Can the engine oil be completely drained during an oil change?

[Weston]

Engine oil cannot be completely drained during an oil change. The steps for changing engine oil are as follows: 1. Run the engine until it reaches operating temperature; 2. Engage the handbrake and lift the vehicle; 3. Unscrew the oil filter and drain the oil; 4. Apply new oil to the gasket of the new filter; 5. Pour the new oil into the oil pan; 6. Check for leaks under the engine; 7. Lower the vehicle, check the oil dipstick, and start the engine; 8. Turn off the engine and recheck the oil level. The functions of engine oil include: 1. Acting as a rust inhibitor: Neutralizing acidic substances produced by combustion gases to prevent engine rust and corrosion; 2. Acting as a cleaner: Preventing pollutants and oxide impurities generated during combustion from adhering to the engine internals, thus maintaining cleanliness; 3. Acting as a coolant: Absorbing heat generated in the engine combustion chamber and piston crowns to cool the engine.

[McJayla]

Is it really possible to completely drain old oil during an oil change? In my practice, this is nearly impossible due to the complex internal structure of the engine. For example, the oil pan is the main drainage point, but oil adheres to engine walls, oil passages, and component gaps—especially in curved or hidden areas. Even after draining for hours, some residue remains. I've handled many cases for car owners and found that even with high-quality draining tools, residue can reach 5-10%. This may seem minor, but it affects the performance of the new oil. If you frequently drive short distances or operate in high-temperature environments, this residue accelerates sludge formation, ultimately damaging engine longevity. I recommend using a specialized flush product during each oil change to help loosen residue, or scheduling periodic professional cleaning at a repair shop. While 100% cleanliness isn't achievable, extra effort extends vehicle health and saves unnecessary costs. Don't overlook this small detail—it impacts overall driving safety.