How Long Can Motor Oil Last After Opening the Cap?
3 Answers
Motor oil can last for about half a year after opening the cap. Beyond this period, the oil may deteriorate, leading to a decline in lubrication performance. Motor oil, engine oil, or engine lubricant is a substance enhanced with additives in base oil, primarily containing anti-wear additives, detergents, dispersants, and multi-grade oil viscosity index improvers. Motor oil is used for lubricating internal combustion engines, with its main functions being to reduce friction and wear on moving parts and to remove sludge and varnish from the engine. Methods for preserving motor oil: 1. After maintenance, the remaining oil should be sealed with the cap as soon as possible, preferably sealed with wax; 2. Motor oil is prone to deterioration under light and high temperatures, so the leftover oil should be stored in a cool and dry place to prevent accelerated deterioration; 3. It is recommended to use up the remaining oil within half a year.
Last year when I did my own car maintenance, I had half a bucket of engine oil left. I sealed the lid and stored it in a corner of the garage, leaving it there for almost 10 months before using it again. After adding the old oil, I felt the engine didn’t start smoothly. Consulting a professional, I learned that opened engine oil oxidizes and absorbs moisture when exposed to air, significantly reducing its lubricating performance. It’s generally recommended not to use it beyond six months. Now I’ve learned my lesson—I always label the opened oil with the date and try to use it within three months. When storing, I keep it away from light and moisture, placing it on a wooden shelf in the basement for safety, which can extend its shelf life a bit. However, it’s best not to risk storing it for too long to avoid damaging the car. Any excess oil can be used for small tasks like lubricating bicycle chains, ensuring nothing goes to waste.
As a driver with years of experience, I've encountered a similar situation where I didn't use up the engine oil in time after opening the bottle. It was stored for about 8 months before being added to the engine, and subsequent inspection revealed slight sludge formation. Opened engine oil is prone to moisture absorption and oxidation, with an optimal storage period of within six months. Keeping it well-sealed in a cool place can extend its shelf life a bit. I recommend cleaning the bottle opening before tightly resealing it each time to prevent dust from affecting the oil quality. Never use oil that's been opened for over a year to avoid corroding the cylinder walls. If there's only a small amount of oil left, it's better to dispose of it and get fresh oil for peace of mind, as engine repairs can be extremely costly and regrettable.
