Can different motor oils be mixed?
2 Answers
Motor oils should not be mixed. Used oil in old motor oil contains a large amount of oxidizing substances. When new oil is mixed with old oil, the oxidation rate of the new oil will increase, thereby reducing the service life and performance of the new oil. Motor oil, engine oil, or engine lubricant is a substance enhanced with additives in base oil, mainly containing anti-wear additives, detergents, dispersants, and multi-grade oil viscosity index improvers. The main functions of motor oil are to reduce friction and wear of moving parts, remove sludge and varnish in the engine, neutralize acids produced by fuel and lubricant oxidation, improve the sealing of piston rings, and cool the engine by carrying away heat from moving parts.
When I first bought my car last year, I also wondered if engine oils could be mixed, thinking it was a waste to leave some oil unused. Once when my car's oil level was low, a friend handed me a bottle of a different brand, and I added it in. A few days later, the engine suddenly started making rattling noises. I took it to the repair shop, and the mechanic said the mixed oil had damaged the lubrication layer, causing severe wear on the parts, costing me several hundred bucks to fix. Now I understand that different brands of oil have different formulations. Mixing base oils and additives might cause chemical reactions, leading to uneven viscosity or sedimentation, which affects engine lifespan. I suggest everyone completely drain the old oil when changing it, use a single brand and the same model, and don’t cut corners for convenience. Regularly check the dipstick to keep the oil level within the normal range—that way, your car runs smoothly and worry-free.
