What are the methods to determine when engine oil needs to be replaced?

[Caleb]

Engine oil needs to be replaced when: 1. The vehicle's power decreases and acceleration becomes sluggish; 2. Upon opening the hood and pulling out the dipstick, a strong sour or foul odor is detected; 3. When examining oil droplets on the dipstick under strong light, check for any impurities mixed in; 4. Take a small amount of used oil between your fingers and rub it repeatedly—if it feels less viscous, contains granular impurities, or even feels gritty, it's time for a change. The method for replacing engine oil is: 1. Run the engine until it reaches operating temperature; 2. Place an old oil container under the oil pan and loosen the drain plug; 3. Move the oil container under the oil filter and unscrew the filter element; 4. Apply some new oil to the gasket of the filter element; 5. Pour the new oil into the oil pan.