When should I change my oil?

When an engine is not running, the oil collects in an oil pan or sump at the bottom of the crankcase. There is an oil drain plug normally screwed into a drain hole at the bottom of the oil pan which is accessible from underneath the vehicle. To change the oil in a vehicle's engine, the drain plug is unscrewed to let the oil drain out of the oil pan. After the used oil drains out, the plug is screwed back into the drain hole. Some drain plugs have a replaceable washer to prevent leakage due to corrosion, rust or worn threads in the drain hole. The removable oil filter can be unscrewed at this time, often with the help of an oil filter removal tool, People who don't posses a filter removal tool, often like to use a screwdriver, which is pierced through the (thin) filter and then used as a lever, making it easy to unscrew the filter. (Some, however, oppose this practice, for the reason that if it should still prove impossible to remove the filter by these means, the car will have been immobilised as a result of piercing it.) Then a new oil filter screwed back in after applying fresh oil to the sealing surface of the new filter. Then new oil is poured in through an otherwise capped opening at the top of the engine. For many cars, 4 to 5 quarts or liters of oil are needed to fill the engine. In the engine, there is a removable dipstick, accessible from above the engine, to check the oil level while engine is not running. (In contrast, automatic transmission fluid level is checked with a separate dipstick while the engine is running.) Traditionally, lubrication at various joints in the vehicle is also done at the time of an oil change. Mechanics often call this maintenance routine "oil change and lube" or "LOF" (lube, oil, and filter).