Can the remaining engine oil from maintenance be used next time?
3 Answers
The unused engine oil can be used during the next oil change. Engine oil shelf life: Unopened engine oil has a shelf life of 4-5 years, and even after opening, it can be stored for one to two years if sealed properly. Typically, high-quality engine oil contains no more than 0.03% water content. If the water content exceeds 0.03%, the effectiveness of the oil will gradually diminish. When the water content exceeds 0.1%, the oil becomes completely unusable. Beware of oil oxidation: Engine oil contains a large amount of antioxidants and detergents, which are very unstable and prone to chemical reactions with oxygen in the air, especially when exposed to sunlight, accelerating the deterioration of the oil.
As a car enthusiast, I always save a small half bottle of oil after each oil change, which can indeed be used for the next maintenance. The key lies in the storage method: wipe the bottle mouth clean, tighten the cap, then wrap a layer of plastic wrap to prevent air leakage, and store it in a cool and dry garage for the safest. In the past, I just casually threw it in the trunk, and the oil absorbed moisture and turned cloudy. Now, I always attach a date label to remind myself not to exceed one year, as additives will lose effectiveness after being opened for too long. Mixing with new oil is fine, but make sure it's the same brand and model. Last year, I once mixed different brands, and the engine sound became abnormal. However, if metal shavings are found in the oil, discard it without hesitation.
I maintain both of our family cars by myself, and the saved-up engine oil over a year is enough for a minor service. The key lies in sealing—tighten the threaded cap of the oil bottle until it clicks, then store it in a Lock&Lock box tucked away in the corner of the storage cabinet, away from the air vents. Before each oil change, shake the bottle to check its flow state—if it's clear like new oil, it's good to use. The worst fear is mixing in coolant; if there are water droplets inside the oil cap, it's ruined. Last week, I just used the leftover 0W-20 oil from last year to change the oil for the Civic, mixing it with the newly purchased batch from the same lot, and everything worked fine. If your car uses less oil, the leftovers from three changes can accumulate enough for one service—little by little does the trick.
