What are the effects of not completely draining old engine oil?
2 Answers
Small amounts of residual old engine oil have minimal impact. When changing the engine oil, it is common practice to replace both the oil and the oil filter simultaneously. The newly added oil can dilute the old oil remaining in the engine, and installing a new oil filter helps remove impurities from the old oil. Typically, there are two methods for changing engine oil: one involves draining the used oil through the oil pan drain plug, and the other uses an oil extractor to suction out the used oil from the dipstick tube. Both methods may leave some residual used oil in the engine due to its complex internal structure, but these small amounts of leftover old oil generally do not cause significant issues.
Incomplete draining of old engine oil has significant consequences. Residual old oil mixes with fresh oil, carrying contaminants like carbon deposits, metal particles, and acidic substances that degrade the new oil's lubricating properties. During engine operation, critical friction components such as pistons and bearings receive inadequate protection, leading to accelerated wear, increased noise, and potential fuel consumption rise. Prolonged neglect causes sludge buildup that clogs oil passages, heightening overheating risks and shortening engine lifespan – eventual repairs can be costly. I've personally experienced this: my car lost power, and subsequent inspection revealed blackened, degraded oil. For oil changes, choose professional shops that perform thorough draining or learn to use oil extraction equipment yourself to ensure complete removal before refilling. Regular maintenance is crucial – don't let minor oversights drain your wallet.
