Can Different Engine Oils Be Mixed?
4 Answers
Generally, mixing engine oils should be avoided as much as possible. More information about mixing engine oils is as follows: 1. Theoretically, oils of the same type can be mixed because they share the same base oil and can lubricate, clean, cool, seal, reduce friction, prevent rust, and protect against corrosion in the engine. 2. However, in reality, the additive compositions in oils from different manufacturers may vary completely, and even different product lines from the same brand may have different chemical compositions. When oils from any two brands are mixed, chemical reactions may occur under the high temperatures of the engine. Therefore, it is recommended not to mix oils from different brands.
As a car owner who frequently performs DIY maintenance, I genuinely don't recommend mixing motor oils. The base oil formulations and additive packages vary significantly between different brands or types of oils. Mixing them may cause abnormal chemical reactions, such as additive conflicts leading to sludge formation or foaming, which compromises lubrication effectiveness. This not only increases engine noise and fuel consumption but may also cause long-term wear and shorten engine lifespan. I once had to mix a small amount of different brand oil in an emergency oil shortage situation - while no immediate issues occurred, I completely replaced it before the next oil change. It's best to stick with the same oil product, or at least ensure compatibility between old and new oils (such as matching API ratings). If mixing is absolutely necessary, prioritize blending small amounts of the same type (synthetic with synthetic or mineral with mineral) for emergency use, then perform a full oil change ASAP. Regular maintenance using manufacturer-recommended oil remains the safest and most reliable approach.
As a car enthusiast, engine oil formulation is not just a simple liquid. Synthetic and mineral base oils differ fundamentally, and when mixed with special additives like detergents and antioxidants, the chemical balance can be disrupted. Some oils experience significant viscosity changes when mixed, leading to uneven lubrication and increased component friction. I've seen a friend's engine overheat and trigger a warning after mixing oils, with diagnostics showing poor oil flow. Compatibility depends on API specifications like SN or SP ratings—mismatches can cause failure. For safety, completely drain the old oil when changing and add fresh oil; if mixing is necessary, only do so briefly with products of the same grade. Long-term use of mixed oils can lead to carbon buildup and shorten engine life, so sticking to a single brand is more convenient and reliable.
When I first got my driver's license, I was curious about mixing engine oils to save money, but it resulted in noticeable engine vibrations. The technician explained that mixing different oils can easily cause sedimentation, clogging the filter or reducing oil pressure. This can lead to insufficient power or warning lights coming on. Especially in modern cars with precise sensors that are sensitive to oil quality, mixing oils may trigger false alarms. Simply put, avoiding oil mixing is the safest bet, particularly for turbocharged or high-mileage vehicles. In emergencies, adding a small amount of the same specification oil is acceptable, but you should visit a workshop for a full oil change as soon as possible. New car manuals emphasize using specified oils, and arbitrary mixing may void the warranty.
