How Long Can Opened Engine Oil Be Used?
3 Answers
Opened engine oil can be used for 6 months to 1 year. Below are the specific functions of engine oil: 1. Shock absorption: When the pressure in the engine cylinder rises sharply, it suddenly increases the load on the piston, piston pin, connecting rod, and crankshaft bearings. This load is transmitted and lubricated through the bearings, providing a cushioning effect against impact loads. 2. Rust and corrosion prevention: The lubricating oil adheres to the surface of parts, preventing contact with water, air, acidic substances, and harmful gases. 3. Lubrication and wear reduction: There is rapid relative sliding between the piston and cylinder, as well as between the main shaft and bearing shells. To prevent excessive wear, an oil film of sufficient thickness must be established between the sliding surfaces to separate them and reduce wear. 4. Cooling: Engine oil carries heat back to the oil tank and dissipates it into the air, assisting the radiator in cooling the engine.
I remember the first time I bought a bottle of full synthetic engine oil. After opening it, I left it in the garage for half a year and forgot to use it. When I added it to the engine, the car ran like an old ox panting. Upon checking, I found the oil had oxidized and deteriorated, losing its lubricating properties, and the repair cost me nearly a thousand bucks. A hard lesson learned: experts say once engine oil is opened and exposed to air, it absorbs moisture and oxidizes quickly, with a shelf life generally of 6-12 months, even shorter for mineral oil. Now I always stick a note on the bottle with the date, forcing myself to use it within six months, and store it in a cool, dry, and sealed place. Synthetic oil has slightly better heat resistance, but don’t exceed nine months, or the viscosity changes could damage the engine. Here’s a quick check tip: shake the bottle to see if it’s cloudy, and if it smells off, throw it away. Better to waste a bit of money than risk vehicle safety.
I'm an oil enthusiast and often ponder about this. The main reason for accelerated oxidation after opening the oil container is exposure to oxygen, which causes additive breakdown and moisture absorption leading to emulsification and deterioration. Generally, it can last 6-12 months, but it actually affects engine lubrication. I once tried using mineral oil stored for a year, and the engine noise skyrocketed after adding it; later, I switched to full synthetic oil, which remained normal even after eight months of storage. Storage tips: tighten the cap and keep it in a cabinet away from light and moisture. The testing method is simple: pour out a bit and check if the color has darkened or if bubbles form, which indicates spoilage. Different oil types vary significantly: synthetic oil has better oxidation resistance, while mineral oil deteriorates more easily. In short, for your car's health, don't delay too long and perform regular checks.
