Is It Safe to Mix Different Oils in Your Engine?

When it comes to engine oils, questions often arise about mixing different brands or types, such as synthetic and conventional oils. The short answer is yes, you can mix them, but there are crucial considerations to keep in mind for optimal engine performance and longevity.

Compatibility: Mixing Brands and Types

It's generally safe to mix oils from different brands or types. For example, blending Mobil 1 with AMSOIL or combining synthetic and conventional oils is permissible. Many modern synthetic oils are fully compatible with conventional counterparts. However, a synthetic blend—combining synthetic and conventional oils—already exists.

The Caveat: Why You Should Think Twice

While it's technically possible, it's not always advisable to mix oils. AMSOIL, for instance, supports compatibility but warns against extended drain intervals after mixing oils. The reason lies in the carefully crafted 'oil formulation' that includes specific base oils and additives unique to each brand and type.

Delicate Balance of Formulation

Oil companies meticulously select base oils and additives, creating a proprietary blend for each brand and type. This balance is crucial for achieving desired performance characteristics. Mixing oils disrupts this equilibrium, potentially affecting the effectiveness of additives that work synergistically.

Avoid Aftermarket Additives

Adding aftermarket oil additives is generally discouraged. These additives, such as "Slick 50" or "Prolong," can interfere with the carefully formulated additives already present in the motor oil. The risk involves upsetting the balance, leading to potential degradation of oil quality and performance.

Potential Issues: Corrosion and Unintended Reactions

Increasing the concentration of one additive might improve one property while degrading another. For example, a high concentration of an anti-wear agent could impact the effectiveness of a corrosion inhibitor. This imbalance can result in corrosion-related problems, affecting overall oil quality.

Best Practices for Mixing Oils

While mixing compatible oils won't cause catastrophic engine failure, it can compromise lubricant performance. To minimize negative effects:

• Choose the Same Brand and Formulation: Opt for oils of the same brand, formulation, and API Service Classification Rating when mixing.
• Avoid Aftermarket Additives: Stick to the manufacturer's recommended oil without introducing aftermarket additives.

By following these guidelines, you ensure that your engine continues to run smoothly without sacrificing the performance and longevity of your motor oil.